Cancer Causes Control (2014) 25:829–841 DOI 10.1007/s10552-014-0384-4

ORIGINAL PAPER

Occupational exposure and ovarian cancer risk Nhu D. Le • Andy Leung • Angela Brooks-Wilson Richard P. Gallagher • Kenneth D. Swenerton • Paul A. Demers • Linda S. Cook



Received: 3 December 2013 / Accepted: 3 April 2014 / Published online: 12 April 2014 Ó Springer International Publishing Switzerland 2014

Abstract Purpose Relatively little work has been done concerning occupational risk factors in ovarian cancer. Although studies conducted in occupational settings have reported positive associations, their usefulness is generally limited by the lack of information on important confounders. In a populationbased case–control study, we assessed risk for developing epithelial ovarian cancer (EOC) associated with occupational exposure while accounting for important confounders. Methods Participants were identified through provincial population-based registries. Lifetime occupational history and information on potential confounding factors were obtained through a self-administered questionnaire. Unconditional logistic regression and the likelihood ratio test were used to assess EOC risk with each occupation (or industry), relative to all other occupations (or industries), adjusting for potential confounders including body mass

N. D. Le (&)  A. Leung  A. Brooks-Wilson  R. P. Gallagher Cancer Control Research, BC Cancer Research Centre, 675 W. 10th Ave, Vancouver, BC V5Z 1L3, Canada e-mail: [email protected] A. Brooks-Wilson Canada’s Michael Smith Genome Sciences Centre, BC Cancer Agency, 600 W. 10th Ave, Vancouver, BC V5Z 4E6, Canada K. D. Swenerton Medical Oncology, BC Cancer Agency, 600 W. 10th Ave, Vancouver, BC V5Z 4E6, Canada

index, oral contraceptive use, menopausal hormone therapy, parity, age at first childbirth, age at menarche, age at menopause, family history of breast and ovarian cancer in mother and sister(s), tubal ligation, partial oophorectomy, and hysterectomy. Occupations and industries were coded according to the Canadian Standard Occupational Classification (SOC) and Standard Industrial Classification (SIC). Results Significant excess risk was observed for several groups of teaching occupations, including SOC 27, teaching and related (adjusted OR 1.77, 95 % CI 1.15–2.81) and SOC 279, other teaching and related (adjusted OR 3.11, 95 % CI 1.35–8.49). Significant excess was also seen for a four-digit occupational group SOC 4131, bookkeepers and accounting clerks (adjusted OR 2.80, 95 % CI 1.30–6.80). Industrial sub-groups showing significant excess risk included SIC 65, other retail stores (adjusted OR 2.19, 95 % CI 1.16–4.38); SIC 85, educational service (adjusted OR 1.45, 95 % CI 1.00–2.13); and SIC 863, non-institutional health services (adjusted OR 2.54, 95 % CI 1.13–6.52). Conclusions Our study found an elevated EOC risk for teaching occupations and is the first study to observe such an increased risk after adjustment for potential confounders. Further studies with more detailed assessment of the work environment and unique lifestyle characteristics may be fruitful in elucidating this etiology. Keywords Epithelial ovarian cancer  Occupational risk  Job history  Case–control study

P. A. Demers Occupational Cancer Research Centre, Cancer Care Ontario, 505 University Ave., Toronto, ON M5G 1X3, Canada

Introduction

L. S. Cook Department of Internal Medicine, University of New Mexico, MSC 10 5550, Albuquerque, NM 87131-0001, USA

Ovarian cancer is the sixth most common malignancy among women in the world, accounting for approximately 4 % of all female cancers [1]. Ovarian cancer has the

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highest mortality rate of all the gynecological malignancies [2]. In Canada and in the USA, it is estimated that 2,600 and 22,240 new cases were diagnosed, together with 1,750 and 15,550 deaths, respectively, in 2012 [3, 4], the majority ([85 %) being of epithelial origin. Despite the high incidence and mortality rates, the etiology of this cancer is still uncertain [5]. Several non-occupational factors have been established as being related to its development. A reduction in ovarian cancer risk has been found with several reproductive factors such as high parity [6, 7], and the use of oral contraceptives [8–11], as well as with gynecologic surgeries such as oophorectomy, hysterectomy, and tubal ligation [12, 13]. An increased risk has been observed for women with a family history of ovarian cancer [14]. Mutations in BRCA1 and BRCA2 genes have been associated with the majority of hereditary ovarian malignancies [15]. Other possible risk factors include use of hormone therapy, early age of menarche, late age of menopause, infertility, obesity, diet, and physical inactivity [5]. Relatively little work has been done concerning workplace-related risk factors in ovarian cancer [16]. With respect to occupations, a recent cohort study of Norwegian nurses revealed an increased risk for developing ovarian cancer [17]. Proportional mortality studies using death registrations, in both Canada and the USA, have shown elevated risks of ovarian cancer in teachers and nurses [18–20]. Other mortality studies of registered nurses and teachers indicated a similar positive association [21, 22]. However, these studies did not adjust for important factors such as parity, oral contraceptive use and gynaecological surgeries; thus, it has been suggested that the observed excess risk may be due to the absence of these protective factors [23]. With respect to specific occupational exposures, several studies from around the world have found an excess mortality risk for hairdressers and beauticians [24–28], suggesting that hair dyes or other agents commonly used in this occupation may have an etiologic role [29, 30]. Two recent meta-analysis studies have shown excess incidence and mortality risk for long-term exposure to asbestos [31, 32]. An elevated occurrence of ovarian cancer has been observed among women exposed to ionizing radiation [33–35]. Excess mortality risk has also been observed in women employed in the telephone industry, with potential exposure to ionizing radiation [36]. Female workers in several industries have been observed to have an increased risk for ovarian cancer, including aerospace [37], textile [38], printing [39], and pulp and paper [40]. Suspected exposures include trichloroethylene for the aerospace industry, silica dust for textile, and asbestos-contaminated talc fillers for printing and pulp/paper industries. One limitation of all these studies is the lack of adjustment for well-established risk factors and the potential misclassification of the diagnoses from peritoneal mesotheliomas. Indeed, many authors correctly cautioned

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that confounding factors such as socioeconomic status, parity, gynaecological surgeries and other lifestyle factors were not directly accounted for in their studies, and such confounding may explain the observed associations. In this population-based case–control study, we specifically examined the occupational risk for epithelial ovarian cancer, using a lifetime work history while accounting for important confounders (e.g., parity, oral contraceptive use, etc.) for each individual.

Methods Cancer cases were women aged 20–79 years, diagnosed with invasive and borderline ovarian cancer diagnosed between January 2001 and December 2007, and identified through the BC Cancer Registry (BCCR). The BCCR is a population-based cancer registry which has been monitoring the occurrence of cancer in a defined population of approximately 4.1 million residents in British Columbia since 1969. Pathology reports detailing newly diagnosed cancer cases are submitted to the BCCR from every hospital and regional pathology service throughout the province. Accurate documentation on histology is available in at least 95 % of all incident cases, and ascertainment for most cancer sites is considered virtually complete. Deceased patients were excluded in this study. Although their inclusion would increase the number of participants, our experience [41] has been that information provided by proxy respondents on occupational history is not reliable. Controls, aged 20–79, were selected from the general population through the Client Registry of the BC Ministry of Health. The registry covers approximately 99 % of the BC population above age 20, including all subscribers of the BC Medical Services Plan. Recorded data include family name, given name, age, sex, mailing address, postal code, and phone number. Controls with cancer history (except basal or squamous cell carcinoma of the skin) were not eligible for this study. Cases and controls were asked to complete a selfadministered questionnaire with questions on lifetime employment history of all jobs held at least for 3 months, along with job descriptions; detailed reproductive history, including age at menarche and menopause, use of fertility drugs, tubal ligation, history of hysterectomy with/out partial oophorectomy, oral contraceptive and menopausal hormone use; detailed family history of cancer; and demographic characteristics. Returned questionnaires were individually reviewed, and participants were called to obtain missing information and/or to clarify ambiguous answers. An experienced coder performed the occupational coding using participants’ occupational histories together their job descriptions. The

Cancer Causes Control (2014) 25:829–841

Canadian Standard Occupational Classification [42] (SOC) and Standard Industrial Classification [43] (SIC) were used to code occupations and industries, respectively, according to two-, three- and four-digit group codes. The codes are increasingly more specific with two-digit representing major groups, three-digit for minor groups within a major one, and four-digit for units within a minor group. Unconditional logistic regression and likelihood ratio test [44] were the primary analytic tools. Statistical analyses were completed with R software [45]. Occupation risk was examined using a two-step procedure. In step 1, the effect of non-occupational factors, including body mass index, oral contraceptive use, menopausal hormone therapy, parity, age at first childbirth, age at menarche, age at menopause, family history of breast and ovarian cancer in mother and sister(s), tubal ligation, partial oophorectomy, hysterectomy, smoking, alcohol consumption, and education, was assessed. Variables were selected in a backward fashion where a factor was removed if its corresponding p value was greater than 0.2; the process was repeated until all remaining factors had their significance level less than or equal 0.2. In step 2, each occupational and industrial code was assessed separately using the parsimonious model identified in step 1, to account for potential confounding factors. Analyses were conducted for two different estimates of occupational exposures: usual occupation or industry (job with the longest held in lifetime employment in a given occupation or industry) and ever occupation or industry (where a job was ever held for at least 2 years in the occupation under consideration or industry). Adjusted odds ratios (OR) and corresponding 95 % confidence intervals were calculated for occupational and industrial group codes. In all analyses, women with the noted occupation (or industry) were compared with women in all the other occupations (or industries). Statistically significant high ORs or those with at least 50 % excess risk are presented for codes with at least three cases and three controls.

Results Between January 2001 and December 2007, a total of 1,314 eligible cases were successfully contacted; 138 cases died before study contact. Of those contacted, 916 patients (69.7 %) agreed to participate. Among those that participated, 210 (22.9 %) had borderline and 706 (77.1 %) had invasive tumors of which 608 were epithelial ovarian cancer (EOC). Population-based controls were available until early 2005 when new legislation concerning privacy for BC residents resulted in restricted access to this population-based control source for research. During the recruitment period, 727 eligible controls were successfully contacted; 335 (46.1 %) agreed to participate.

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The characteristics of the 608 EOC cases and 335 controls are generally consistent with our current knowledge of EOC risk factors (Table 1). Parity, oral contraceptive use, and gynaecological surgeries were associated with a reduced risk for EOC, whereas a family history of ovarian and breast cancers and the use of menopausal hormonal therapy were associated with an increased risk after adjustment for the other risk factors (Table 2). The risks for EOC associated with both ever and usual occupations, relative to all other occupations, after adjustment for other risk factors are presented in Table 3. Ovarian cancer risk was significantly elevated among those ever involved in teaching occupations (for SOC 27, teaching and related, adjusted OR 1.77, 95 % CI 1.15–2.81 and for SOC 279, other teaching and related, adjusted OR 3.11, 95 % CI 1.35–8.49). While SOC 27 includes all teaching and related occupations, the sub-group SOC 279 consists of teaching occupations in technical, vocational, fine arts schools, and community colleges. When assessed as usual occupation, the risk was slightly attenuated for SOC 27 (adjusted OR 1.61, 95 % CI 0.94–2.88) and could not be estimated reliably for SOC 279 due to small sample size. Usual work as a bookkeeper or accounting clerk was also associated with an elevated risk (SOC 4131, adjusted OR 2.80, 95 % CI 1.30–6.80). Non-significant elevations of 50 % or more in risk were noted for ever work in services management (SOC 1142), accountants, auditors and other financial officers (SOC 1171), university teaching (SOC 271), elementary and secondary teaching (SOC 2739), registered nursing assistants (SOC 3134), other clerical supervisor (SOC 4190), food and beverage preparation supervisors (SOC 6120), lodging cleaners (SOC 6133), product fabricating (SOC 85) and packaging not elsewhere classified (SOC 9317). Non-significant elevations of 50 % or more in risk were noted for usual occupations as well. Such elevations were noted for: accountants, auditors and other financial officers (SOC 1171); teaching occupations (SOC 27); elementary and kindergarten teachers (SOC 2731); therapy and related assisting nursing (SOC 3139); and other occupations in medicine and health (SOC 315). The risks for EOC associated with both ever and usual industries of work, relative to all other industries, are presented in Table 4. Significantly elevated EOC risks were noted for ever work in other retail store industries (SIC 65, adjusted OR 2.19, 95 % CI 1.16–4.38); educational service (SIC 85, adjusted OR 1.45, 95 % CI 1.00–2.13); and non-institutional health services (SIC 863, adjusted OR 2.54, 95 % CI 1.13–6.52). However, when assessed as usual occupation, the risk was completely attenuated for other retail store industries (SIC 65) and could not be estimated reliably for non-institutional health services (SIC 863). Usual work in educational service was

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832 Table 1 Characteristics of cases and controls

Cancer Causes Control (2014) 25:829–841

Characteristic

Cases (n = 608)

Controls (n = 335)

ORa

95 % CI

p value

Age at diagnosis/interview, years \50

142 (23 %)

127 (38 %)

50–65

274 (45 %)

120 (36 %)

C65

192 (32 %)

88 (26 %)

Current body mass index, kg/m2 \25

330 (54 %)

168 (50 %)

1.00

25–30

180 (30 %)

109 (33 %)

0.80

0.59–1.09

0.16

30–35

57 (9 %)

33 (10 %)

0.87

0.54–1.41

0.57

C35

41 (7 %)

24 (7 %)

0.91

0.53–1.58

0.72

328 (54 %) 54 (9 %)

144 (43 %) 27 (8 %)

0.84

0.51–1.43

0.52

2–5

92 (15 %)

69 (21 %)

0.56

0.38–0.82

0.003

C5

134 (22 %)

95 (28 %)

0.66

0.47–0.94

0.02

No

347 (57 %)

231 (69 %)

Yes

261 (43 %)

103 (31 %)

1.47

1.09–1.98

0.01

0

164 (27 %)

56 (17 %)

1.00

1

89 (15 %)

45 (13 %)

0.59

0.36–0.95

0.03

2

190 (31 %)

112 (33 %)

0.45

0.30–0.67 \0.001

C3

161 (26 %)

117 (35 %)

0.31

0.20–0.47 \0.001

164 (27 %)

56 (17 %)

1.00

Duration of OC use (years) Never \2

Ever used hormone therapy

Parity, number of full-term births

Age when first livebirth was given Never \20

0.21–0.57 \0.001

78 (13 %)

54 (17 %)

0.35

20–25

171 (28 %)

111 (34 %)

0.38

0.25–0.58 \0.001

26–30 C30

126 (21 %) 43 (7 %)

66 (20 %) 30 (9 %)

0.50 0.54

0.32–0.78 0.32–0.91

0.002 0.02

0.68–1.94

0.65

0.78–5.29

0.18

Family history of breast cancer (mother) No

559 (92 %)

310 (93 %)

1.00

Yes

48 (8 %)

23 (7 %)

1.13

Family history of ovarian cancer (mother) No

588 (97 %)

328 (98 %)

1.00

Yes

19 (3 %)

6 (2 %)

1.89

180 (30 %)

103 (31 %)

1.00

41 (7 %)

12 (4 %)

1.76

0.90–3.66

0.11

Has sister(s) but none with cancer 376 (62 %) Family history of ovarian cancer (sister)

213 (64 %)

1.01

0.74–1.35

0.97

No sister

Family history of breast cancer (sister) No sister Has sister(s) and at least one with cancer

180 (30 %)

103 (31 %)

1.00

Has sister(s) and at least one with cancer

8 (1 %)

3 (1 %)

1.42

0.39–6.63

0.62

Has sister(s) but none with cancer

409 (67 %)

222 (66 %)

1.04

0.77–1.40

0.79

0.85–1.95

0.25

Family history of breast cancer (first degree relative) No

507 (83 %)

290 (87 %)

1.00

Yes

89 (15 %)

37 (11 %)

1.28

318 (95 %)

1.00

Family history of ovarian cancer (first degree relative) No

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569 (94 %)

Cancer Causes Control (2014) 25:829–841 Table 1 continued

Characteristic

833

Cases (n = 608)

Yes

27 (4 %)

Controls (n = 335) 9 (3 %)

ORa 1.72

95 % CI

p value 0.82–3.96

0.17

At at menarche (years) \12

99 (16 %)

58 (17 %)

1.00

12

152 (25 %)

90 (27 %)

1.01

0.66–1.55

0.95

13

176 (29 %)

88 (26 %)

1.15

0.75–1.75

0.52

C14

149 (25 %)

84 (25 %)

1.02

0.66–1.56

0.94

Age at menopause (years) \45

138 (23 %)

45–50

120 (20 %)

40 (12 %)

1.24

0.78–2.00

0.36

C50

195 (32 %)

95 (28 %)

0.87

0.59–1.29

0.50

Pre-menopause

147 (24 %)

135 (40 %)

0.64

0.38–1.07

0.09

0.23–0.78

0.01

0.60–1.16

0.31

0.48–0.90

0.01

63 (19 %)

Ever had surgeries to partial removal of ovaries No

587 (97 %)

304 (91 %)

1.00

Yes

21 (3 %)

24 (7 %)

0.42

252 (75 %)

1.00

82 (24 %)

0.83

Ever had hysterectomy No 456 (75 %) Yes

151 (25 %)

Ever had tubal ligation No

471 (77 %)

236 (70 %)

1.00

Yes

136 (22 %)

98 (29 %)

0.66

High school or less

249 (41 %)

141 (42 %)

1.00

Vocational school

121 (20 %)

71 (21 %)

1.03

0.72–1.49

0.86

University

238 (39 %)

123 (37 %)

1.28

0.93–1.75

0.12

299 (49 %)

156 (47 %)

1.00

Education

Smoking Never

a b

Current smoker

80 (13 %)

39 (12 %)

1.15

0.75–1.79

0.53

Former smoker

229 (38 %)

140 (42 %)

0.79

0.59–1.06

0.11

0.63–1.17

0.34

Alcohol consumption Age adjusted

Consume \ 12 drinks of beer, wine or hard liquor per year

Nob

170 (28 %)

86 (26 %)

1.00

Yes

437 (72 %)

247 (74 %)

0.86

also associated with an elevated risk (for SIC 85, adjusted OR 1.56, 95 % CI 0.98–2.54). Non-significant excess elevations of 50 % or more in risk were noted for ever work in the following industries: food (SIC 10); book and stationery stores (SIC 651); other retail stores (SIC 659); insurance underwriters (SIC 73); architectural and engineering (SIC 775); federal government services (SIC 81, 811); post-secondary and university education (SIC 852, 853); library services (SIC 854); home care services (SIC 8621, 8634); offices of dentists (SIC 8653); hotels and motels (SIC 911, 9111); licensed restaurants (SIC 9,211); and janitorial services (SIC 9,953). Additionally, usual work in the following industries was associated with non-significant elevations of 50 % or more in risk: business service industries (SIC 77, 775); federal government services (SIC 81); university education (SIC

853); non-institutional social services (SIC 864); offices of physicians, surgeons and dentists (SIC 865); motels and hotels (SIC 9,111); food services (SIC 921); licensed restaurants (SIC 9,211); other household and personal services (SIC 979); and other services (SIC 99).

Discussion In this study, teaching and related work was associated with an elevated risk for EOC. This is consistent with the reported literature [18, 21, 46–48]. It has been suggested that the observed excess risk in these previous studies may be due to the absence of protective factors such as parity, oral contraceptive, and gynaecological surgeries that were not accounted for in the analysis. As far as we are aware,

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Cancer Causes Control (2014) 25:829–841

Table 2 Odds ratios (ORs) for potential confounding variables OR

a

95 % CI

p value

0.018

Parity, number of full-term births 0

1.00

1

0.55

0.33–0.90

2

0.44

0.29–0.67 \0.001

C3

0.29

0.18–0.45 \0.001

Duration of OC use (years) Never

1.00

\2

0.94

0.55–1.63

0.819

2–5

0.56

0.37–0.84

0.005

C5

0.66

0.46–0.95

0.026

Ever used hormone therapy No

1.00

Yes

1.50

1.08–2.10

0.016

0.77–6.62

0.177

Family history of ovarian cancer (mother) No

1.00

Yes

2.07

Family history of breast cancer (sister) No sister

1.00

Has sister(s) and at least one with cancer

2.11

1.04–4.61

0.048

Has sister(s) but none with cancer

1.08

0.78–1.48

0.649

0.17–0.65

0.001

Ever had surgeries to partial removal of ovaries No

1.00

Yes

0.34

Age at menopause (years) \45

1.00

45–50

1.45

0.88–2.41

0.148

C50 Pre-menopause

0.79 0.65

0.52–1.21 0.37–1.14

0.282 0.134

a

Odds ratios are adjusted for age and other variables in the table

our study is the first one to observe such an increased risk after adjusting for potential confounders. It is unclear what additional aspects of this occupational group influence the development of EOC. A significant excess risk was seen for the industry group of non-institutional health services, with participants mostly coming from the home care services sub-group. In addition, a non-significant excess risk was observed for the occupation sub-group of registered nursing assistants. Unlike previous studies that showed excess risk for this occupational group [17, 20–22], known and suspected confounders have been accounted for in this study. Information on nightshift work was unavailable and not adjusted for in this analysis. A recent case–control study has found evidence suggesting an association between shift work and the risk for developing ovarian cancer [49]. Jobs in the health care industry, mostly nursing, had the highest proportion (about 30 %) involving nightshift work which may explain the excess risk seen in this study. However, another

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study reported a null association [50] between EOC risk and rotating nightshift work (defined as 3 or more nightshifts per month). Further studies are needed to elucidate the relationship. In contrast to the findings from some previous studies [24–28], we found no excess risk for the occupational subgroup of barbers, hairdressers, and related occupations. A recent linkage study of Swedish female workers also found that hairdressers and beauticians were not at increased risk [51]. This could be due to changes in types of chemicals used recently in these occupations compared with those used 25–30 years ago. A number of white-collar occupations, including accountants and other financial officers, and in federal government services, as well professional jobs in architecture and engineering industry and office of dentists, general practice, showed non-significant and moderate excess risk for EOC. It is possible that the excess risk seen in these subgroups may be due to the sedentary nature of the jobs as several studies have indicated that those who are sedentary may have an elevated risk for ovarian cancer [52, 53]. This study has several strengths. It is population based with incident cases histologically confirmed. Lifetime occupational history was obtained for all participants and allows for the categorization of usual occupation and industry. The occupational risk was estimated accounting for known and suspected confounders [5]. We fully evaluated a broad spectrum of potential confounding factors and adjusted for the most important confounders for EOC risk in our models, but we cannot rule out the possibility that there is still some unmeasured confounding or residual confounding in our risk estimates. We conducted a sensitivity analysis for the main findings in which potential risk factors not included in the main models were included in secondary analyses to examine their impact on the estimated occupational risk; no substantial effect was seen as the occupational risk estimates remained essentially unchanged. The other limitations of this study are the lack of specific exposure information, the relatively low response rate of the controls, and the possibility that, due to multiple testing, some statistically significant results may have occurred by chance. It has been observed that participation rates for epidemiologic studies have been declining over the last 30 years, especially in recent years, probably due to the proliferation of research studies, including marketing research. However, a recent review provides evidence that the low participation rate should not substantially affect the observed occupation-disease associations [54]. There was a mismatch in the recruitment durations of cases and controls because we had to stop recruitment of controls in 2005. Restricted access to the population-based

Cancer Causes Control (2014) 25:829–841

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Table 3 Multivariate adjusted odds ratios for usual and ever occupations Code

Occupation

Ever occupation Cases

Cont

Usual occupation OR

a

95 % CI

Cases

Cont

ORa

95 % CI

0.95

0.58–1.58

0.82

0.46–1.50

11

Managerial, adminstration and related

111

Officials and administrators unique to government

115

62

0.97

0.67–1.40

55

29

6

5

0.46

0.13–1.78

2

2

113/114

Other managers and administrators

86

50

0.96

0.65–1.45

32

22

1130

General managers and other senior officials

5

3

1.10

0.25–5.66

2

1

1134

Administrators in medicine and health

3

3

0.55

0.09–3.25

0

0

1135

Financial management occupations

6

4

0.94

0.25–3.98

2

0

1137 1142

Sales and advertising management Services management occupations

8 13

7 5

0.50 1.96

0.17–1.55 0.69–6.55

2 4

5 2

1149

Other managers and administrators, N.E.C.

41

25

0.99

0.58–1.74

17

12

0.87

0.40–1.95

117

Occupations related to management and adminstration

35

14

1.08

0.56–2.20

21

5

1.54

0.58–4.92

1171

Accountants, auditors and other financial

26

7

1.89

0.80–5.03

19

4

1.85

0.64–6.81

1179

Occupations related to management and adminstration

7

4

0.59

0.17–2.33

0

1

21

Natural sciences, engineering and mathematics

21

8

1.21

0.52–3.09

11

6

0.94

0.33–2.95

211

Physical sciences

3

3

0.24

0.04–1.36

0

1

213

Life sciences

3

4

0.58

0.10–2.89

2

4

23

Social sciences and related fields

44

25

0.99

0.57–1.74

22

11

1.06

0.48–2.44

231

Occupations in social sciences

8

5

0.72

0.23–2.51

3

2

2311

Economists

4

4

0.48

0.10–2.16

3

1

233

Occupations in social work and related fields

23

15

1.11

0.55–2.33

10

6

1.12

0.38–3.56

2331

Social workers

11

9

1.13

0.43–3.02

4

4

0.82

0.17–3.86

2333

Occupations in welfare and community services

13

5

1.21

0.43–3.96

6

2

234 2343

Occupations in law and jurisprudence Lawyers and notaries

9 5

5 4

0.61 0.37

0.19–2.27 0.08–1.77

8 4

3 2

1.03

0.25–5.35

25

Religion

3

3

0.35

0.06–2.08

2

1

251

Occupations in religion

27

Teaching and related

1.61

0.94–2.88

271

3

3

0.35

0.06-2.08

2

1

106

32

1.77

1.15–2.81

62

19

University teaching and related

14

3

2.06

0.63–9.36

9

1

273

Elementary and secondary school teaching

68

27

1.29

0.79–2.15

44

17

1.28

0.71–2.40

2731

Elementary and kindergarten teachers

40

15

1.29

0.69–2.56

25

8

1.50

0.67–3.72

2733

Secondary school teachers

24

9

1.16

0.53–2.75

13

6

0.98

0.36–2.93

2739

Elementary and secondary school teaching and N.E.C.

12

4

2.21

0.71–8.46

6

1

279

Other teaching and related

37

6

3.11

1.35–8.49

9

1

31

Medicine and health

133

53

1.26

0.87–1.86

91

35

1.24

0.80–1.96

313

Nursing, therapy and related assisting

103

46

1.07

0.71–1.62

75

31

1.11

0.70–1.80

3131

Nurses, registered, graduate, and nurses-in-training

50

29

0.73

0.44–1.25

39

24

0.69

0.39–1.23

3134

Registered nursing assistants

17

4

1.83

0.64–6.60

9

0

3135

Nursing attendants

15

7

0.87

0.34–2.40

8

3

0.88

0.24–4.22

3139 315

Nursing, therapy and related assisting, N.E.C. Other occupations in medicine and health

28 31

10 10

1.40 1.49

0.66–3.20 0.72–3.36

11 12

3 4

1.66 1.52

0.49–7.60 0.49–5.78

3156

Medical laboratory technologists and technicians

10

5

0.73

0.24–2.48

2

3

33

Artistic, literary, recreational and related

30

12

1.36

0.68–2.90

12

5

1.39

0.48–4.65

331

Fine and commercial art, photography and

9

6

0.77

0.26–2.42

5

2

3313

Product and interior designers

3

3

0.53

0.09–3.01

1

1

337

Sports and recreation

4

3

0.85

0.17–4.75

1

2

41

Clerical and related

288

160

0.95

0.71–1.27

186

107

0.89

0.65–1.22

411

Stenographic and typing

89

49

0.85

0.57–1.28

50

23

1.02

0.59–1.79

4111

Secretaries and stenographers

73

40

0.88

0.57–1.37

41

21

0.94

0.53–1.70

123

836

Cancer Causes Control (2014) 25:829–841

Table 3 continued Code

Occupation

Ever occupation Cases

Cont

Usual occupation ORa

95 % CI

Cases

Cont

23

11

0.95

0.45–2.13

9

1

133

63

1.27

0.88–1.83

67

29

ORa

95 % CI

1.43

0.88–2.37

4113

Typists and clerk-typists

413

Bookkeeping, account-recording and related

4130

Supervisors: bookkeeping, account-recording

19

7

1.42

0.58–3.84

9

4

1.10

0.33–4.34

4131

Bookkeepers and accounting clerks

72

30

1.42

0.88–2.32

36

8

2.80

1.30–6.80

4133

Cashiers and tellers

54

31

0.92

0.56–1.53

18

13

0.79

0.36–1.77

4135

Insurance, bank and other finance clerks

12

12

0.67

0.28–1.61

4

4

0.66

0.14–3.03

414

Office machine and electronic equipment operators

11

5

1.11

0.38–3.73

5

1

4141

Office machine operators

5

3

0.79

0.18–3.97

1

1

415

Material recording, scheduling and distributing

10

8

0.73

0.27–2.03

1

4

416

Library, file and correspondence clerks and related

13

7

1.13

0.44–3.13

3

5

0.37

0.07–1.58

4161

Library and file clerks

12

7

1.02

0.39–2.87

2

5

417

Reception, information, mail and message

53

50

0.50

0.32–0.78

20

22

0.48

0.24–0.93

4171

Receptionists and information clerks

36

33

0.53

0.32–0.90

11

16

0.33

0.14–0.75

4175 419

Telephone operators Other clerical and related

15 94

12 47

0.58 1.16

0.25–1.36 0.77–1.75

7 40

5 23

0.89 0.89

0.26–3.25 0.51–1.59

4190

Supervisors: other clerical and related, N.E.C.

14

3

2.02

0.62–9.09

5

1

4193

Travel clerks, ticket, station and freight agents

11

4

1.48

0.45–5.92

9

2

4197

General office clerks

53

34

0.88

0.54–1.45

18

15

0.64

0.30–1.38

4199

Other clerical and related occupations, N.E.C.

15

9

0.85

0.35–2.17

7

4

0.70

0.20–2.82

51

Sales

114

70

0.91

0.64-1.30

47

34

0.78

0.48-1.30

513/514

Sales, commodities

103

60

0.96

0.66–1.41

42

29

0.79

0.47–1.35

5130

Supervisors: sales, commodities

40

18

1.35

0.74–2.56

19

8

1.43

0.60–3.70

5135

Sales clerks and salespersons, commodities, N.E.C.

64

47

0.70

0.46–1.08

19

21

0.48

0.24–0.94

517

Sales, services

14

10

0.80

0.33–1.99

4

5

0.58

0.13–2.44

5171

Insurances sales

3

3

0.53

0.09–3.19

1

1

5172

Real estate sales

61

Services

0.88

0.57–1.35

611

Protective services

612 6120

7

4

1.16

0.33–4.68

2

3

134

86

0.86

0.61–1.22

69

47

6

3

0.84

0.20–4.34

3

1

Food and beverage preparation and related Supervisors: food and beverage preparation and related

60 8

37 3

0.94 1.80

0.59–1.52 0.43–9.75

21 3

18 0

0.73

0.37–1.46

6121

Chefs and cooks

16

13

0.77

0.35–1.71

5

7

0.43

0.12–1.43

6123

Bartenders

5

3

0.88

0.20–4.51

2

2

6125

Food and beverage serving

30

15

1.27

0.64–2.63

8

6

0.89

0.29–2.92

6129

Food and beverage preparation and related, N.E.C.

10

7

0.88

0.32–2.57

2

3

613

Lodging and other accommodation services

17

10

0.78

0.34–1.93

6

4

0.61

0.16–2.67

6130

Supervisors: lodging and other accommodation services

7

7

0.45

0.14–1.42

2

3

6133

Lodging cleaners, except private household

9

3

1.64

0.42–8.35

3

1

614

Personal service

42

32

0.76

0.45–1.29

23

14

1.02

0.50–2.15

6142

Housekeepers, servants and related

10

5

1.07

0.34–3.78

5

2

6143

Barbers, hairdressers and related

16

11

0.79

0.34–1.86

12

6

1.18

0.43–3.57

6147

Child-care

13

16

0.55

0.24–1.22

6

6

0.99

0.30–3.32

619

Other service

25

17

0.97

0.50–1.96

13

9

0.96

0.38–2.54

6191

Janitors, char workers, and cleaners

20

13

1.11

0.52–2.46

9

8

0.86

0.30–2.51

6198

Laboring and other elemental work: other services

3

3

0.43

0.07–2.49

2

1

71 718/719

Farming, horticultural, and animal husbandry Other farming, horticultural, and animal

29 25

17 16

0.89 0.79

0.47–1.75 0.40–1.60

10 8

5 4

1.18 1.17

0.39–4.03 0.34–4.69

7195

Nursery and related

4

5

0.45

0.10–1.85

1

0

123

Cancer Causes Control (2014) 25:829–841

837

Table 3 continued Code

Occupation

Ever occupation Cases

Cont

Usual occupation ORa

95 % CI

Cases

Cont

7

6

0.54

0.17–1.78

2

3

12

12

0.55

0.23–1.33

5

5

6

4

0.86

0.23–3.55

3

1

33

8

1.85

0.85–4.49

8

1

7

1.01

0.40–2.78

6

1

ORa

95 % CI

0.53

0.14–2.02

7199

Other farming, horticultural and animal

82

Processing

821/822

Food, beverage and related processing

85

Product fabricating, assembling and repairing

855/856

Fab., assem., and repair textiles, fur, leather

16

91

Transport equipment operating

8

4

1.02

0.30–4.07

4

3

0.48

0.10–2.62

917

Motor transport, other transport equip

6

4

0.71

0.19–3.00

4

3

0.48

0.10–2.62

93

Material handling and related, N.E.C.

13

6

1.19

0.44–3.56

4

2

9317

Packaging, N.E.C.

12

3

2.23

0.67–10.11

4

2

Reference group: All other occupations adjusted for age, parity, oral contraceptive use, family history, hormone therapy, partial removal of ovaries, age at menopause

a

Table 4 Multivariate adjusted odds ratios for usual and ever industry Code

Industry

Ever industry Cases

Usual industry 95 % CI

Cases

Cont

ORa

95 % CI

0.93

0.45–1.97

11

6

1.03

0.37–3.14

1.14

0.28–5.67

6

1

Cont

OR

24

13

7

3

a

01

Agricultural industries

011

Livestock farms

015

Fruit and other vegetable farms

11

4

1.45

0.47–5.50

3

1

0151

Fruit farms

7

4

0.96

0.27–3.93

3

1

02

Service industries incidental to agriculture

4

4

0.54

0.12–2.48

1

2

10

Food

17

7

1.54

0.61–4.31

5

3

1.39

0.30–7.52

25 251

Wood Sawmill, planning mill and shingle mill products

12 7

6 4

0.90 0.88

0.32–2.80 0.23–3.76

6 3

3 2

0.94

0.22–4.90

2512

Sawmill and planning mill products(except shingles, shakes)

28

Printing, publishing, and allied industries

0.99

0.24–5.07

284

1.08

0.33–4.23

6

3

1.01

0.23–5.28

3

1

14

9

0.74

0.31–1.89

6

3

Combined publishing and printing

5

6

0.36

0.10–1.24

2

3

33

Electrical and electronic products

9

3

1.11

0.31–5.24

0

1

37

Chemical and chemical products

5

3

0.56

0.13–2.93

3

0

39

Other manufacturing

8

4

0.88

0.25–3.50

3

0

42

Trade contracting

45

Transportation

451 4511 48

5

4

0.67

0.16–2.98

4

2

23

10

1.34

0.61–3.15

10

4

Air transport

6

3

1.07

0.26–5.46

3

1

Scheduled air transport

4

3

0.75

0.15–4.20

2

1

Communications

25

17

0.81

0.42–1.60

10

11

0.53

0.21–1.34

482

Telecommunication carriers

15

13

0.60

0.27–1.35

8

10

0.41

0.15–1.12

49

Other utilities industries

9

6

0.78

0.26–2.53

3

2

56 57

Metal, hardware, plumbing, heating, building, and wholesale Machinery, equipment and supplies, and wholesale

6 5

3 4

0.90 0.68

0.22–4.49 0.17–3.04

3 0

2 3

60

Food, beverage, and drug industries, retail

40

29

0.75

0.44–1.28

9

17

0.31

0.12–0.70

601

Food stores

34

20

1.00

0.55–1.86

7

12

0.34

0.12–0.88

6011

Food (groceries) stores

23

18

0.75

0.38–1.49

6

10

0.36

0.12–1.03

603

Prescription drugs and patent medicine stores

6

7

0.44

0.13–1.38

2

5

6031

Pharmacies

5

7

0.36

0.10–1.19

2

5

61

Shoe, apparel, fabric and yarn, retail

23

10

1.35

0.61–3.15

8

4

1.15

0.33–4.65

123

838

Cancer Causes Control (2014) 25:829–841

Table 4 continued Code

Industry

Ever industry Cases

Cont

Usual industry ORa

95 % CI

Cases

Cont

ORa

95 % CI

0.48

0.08–2.83

0.61

0.14–2.81

613

Women’s clothing stores

9

4

0.89

0.27–3.49

3

3

614

Clothing stores, N.E.C.

7

4

1.19

0.32–4.96

3

1

15

13

0.66

0.29–1.49

5

4

7

6

0.60

0.18–2.03

2

3

63

Automotive vehicle, parts and accessories

631

Automobile dealers

633

Gasoline service stations

3

4

0.45

0.07–2.36

2

1

64

General retail merchandising industries

46

28

0.78

0.47–1.34

27

13

1.30

0.65–2.74

6411

Department stores

37

24

0.75

0.43–1.35

21

12

1.11

0.52–2.46

65

Other retail store industries

44

14

2.19

1.16–4.38

10

6

1.10

0.37–3.57

651

Book and stationery stores

9

3

2.19

0.62–10.23

1

1

659

Other retail stores

10

4

1.58

0.48–6.16

5

2

70

Deposit accepting intermediaries

47

31

0.84

0.51–1.42

27

19

0.79

0.41–1.53

702

Chartered banks, other banking-type

40

29

0.75

0.44–1.31

22

15

0.85

0.41–1.79

703

Trust companies

4

4

0.69

0.15–3.17

0

4

72 73

Investment intermediaries Insurance underwriters

8 12

3 3

1.39 2.50

0.36–6.87 0.70–11.91

2 5

0 3

1.29

0.27–7.15

75

Real estate operator (except developers)

11

5

0.89

0.30–3.01

4

4

0.47

0.10–2.19

7511

Operators of residential buildings and dwellings

9

4

0.88

0.26–3.53

4

3

0.67

0.13–3.80

76

Insurance and real estate agent industries

32

18

1.04

0.56–1.99

12

8

0.75

0.29–2.02

77

Business service industries

75

29

1.33

0.83–2.18

37

12

1.55

0.78–3.25

775

Architectural, engineering, other scientific/technical

21

5

1.96

0.74–6.21

13

3

1.79

0.52–8.36

776

Offices of lawyers and notaries

19

11

0.86

0.38–2.00

12

5

1.29

0.44–4.29

779

Other business services

22

8

1.19

0.52–3.00

6

3

1.27

0.31–6.36

7799

Other business services, N.E.C.

16

7

0.93

0.38–2.52

5

2

79

General office, N.E.C.

16

10

0.76

0.33–1.83

6

2

81

Federal government service

32

11

1.79

0.87–3.94

15

3

3.26

0.94–15.68

811

Defense services

13

4

1.75

0.56–6.76

7

0

812

Protective services

3

4

0.54

0.09–2.88

2

2

82

Provincial and territorial government services

42

29

0.68

0.40–1.16

21

17

0.54

0.26–1.10

822 825

Protective services General administrative services

8 10

4 10

0.84 0.54

0.23–3.58 0.20–1.41

3 5

1 6

0.43

0.11–1.56

8259

Other general administrative services

8

9

0.45

0.16–1.28

4

5

0.40

0.09–1.68

826

Human resource adminstration

13

10

0.58

0.24–1.49

7

6

0.42

0.13–1.41

8261

Health adminstration

3

6

0.21

0.04–0.93

2

3

8262

Social service adminstration

8

5

0.64

0.19–2.30

5

3

0.71

0.16–3.74

827

Economic services adminstration

14

9

0.79

0.32–2.01

5

4

0.71

0.17–3.11

8272

Resource conservation and industrial

6

5

0.73

0.20–2.75

0

3

83

Local government service industries

21

11

1.12

0.51–2.57

10

4

1.42

0.42–5.72

835

General administrative services

10

7

0.73

0.26–2.15

6

2

836

Human resource adminstration

7

4

0.99

0.27–4.13

3

2

84

International, other extra-territorial government services

85

Educational service

851

5

7

0.19

0.05–0.65

0

1

134

51

1.45

1.00–2.13

86

28

1.56

0.98–2.54

Elementary and secondary education

91

36

1.37

0.89–2.14

61

22

1.38

0.82–2.41

852

Post-secondary non-university education

22

7

1.69

0.71–4.50

5

0

853

University education

24

6

1.81

0.74–5.11

11

3

1.78

0.52–8.17

854 859

Library services Other educational services

9 8

3 3

1.50 1.38

0.41–7.17 0.36–6.72

3 4

2 1

86

Health and social service

191

90

1.16

0.85–1.61

130

58

1.19

0.82–1.73

123

Cancer Causes Control (2014) 25:829–841

839

Table 4 continued Code

Industry

Ever industry

Usual industry

Cases

Cont

ORa

95 % CI

Cases

Cont

ORa

95 % CI

861

Hospitals

104

56

0.83

0.57–1.23

63

39

0.69

0.44–1.10

8611

General hospital

95

49

0.89

0.60–1.35

54

31

0.81

0.49–1.35

8613

Extended care hospitals

11

6

0.70

0.25–2.16

3

4

0.18

0.03–0.93

8617

Children’s (pediatric) hospitals

4

3

0.67

0.13–3.85

0

1

8619

Other specialty hospitals

3

4

0.29

0.05–1.52

1

1

862

Other institutional health and social services

26

18

0.89

0.46–1.77

11

5

1.26

0.42–4.31

8621

Homes for personal and nursing care

18

7

1.54

0.61–4.32

9

1

8624

Homes for mentally handicapped and or disabled

3

4

0.55

0.10–2.71

0

1

8629

Other institutional health and social services, N.E.C.

4

5

0.73

0.17–2.94

1

2

863

Non-institutional health services

31

7

2.54

1.13–6.52

16

1

8634

Home care services (including home nursing)

17

4

2.19

0.78–7.83

11

1

864

Non-institutional social services

27

15

0.89

0.45–1.82

16

4

2.32

0.80–8.50

8641

Child day-care and nursery school services

9

5

0.95

0.30–3.35

7

4

1.07

0.29–4.44

8645 865

Home-maker services Offices of physicians, surgeons and

12 33

10 14

0.63 1.29

0.25–1.62 0.67–2.61

8 18

1 5

2.27

0.85–7.19

8651

Offices of physicians, general practice

15

9

0.96

0.40–2.40

8

4

1.28

0.37–5.11

8653

Offices of dentists, general practice

13

5

1.50

0.53–4.91

7

1

866

Offices of other health practitioners

6

3

1.31

0.32–6.71

3

1

91

Accommodation service industries

42

16

1.23

0.67–2.37

16

8

0.99

0.40–2.64

911

Hotels, motels, and tourist courts

42

12

1.73

0.88–3.62

16

6

1.44

0.54–4.35

9111

Hotels and motor hotels

30

10

1.50

0.71–3.43

13

5

1.50

0.52–5.11

92

Food and beverage service

47

25

1.26

0.73–2.20

15

6

1.75

0.66–5.23

921

Food services

47

23

1.39

0.80–2.49

15

5

2.16

0.77–7.08

9211

Restaurants, licensed

30

14

1.51

0.77–3.10

10

4

1.94

0.60–7.53

9212

Restaurants, unlicensed (including drive-ins)

12

8

1.03

0.38–2.93

4

1

922

Taverns, bars, and night clubs

96

Amusement and recreational services

0.57

0.21–1.60

965

Sports and recreation clubs and services

97 971

4

3

1.17

0.24–6.45

0

1

18

11

0.97

0.43–2.26

10

8

5

6

0.49

0.13–1.75

1

4

Personal and household services Barber and beauty shops

39 15

31 9

0.76 0.95

0.45–1.29 0.39–2.41

22 10

12 5

1.25 1.09

0.59–2.73 0.36–3.68

9712

Beauty shops

13

9

0.83

0.33–2.16

9

5

1.00

0.32–3.43

974

Private households

7

5

0.90

0.26–3.33

3

3

0.58

0.10–3.50

979

Other personal and household services

12

14

0.57

0.24–1.32

7

3

2.07

0.54–10.03

98

Membership organizations

17

10

0.84

0.37–2.01

4

5

0.29

0.07–1.19

981

Religious organizations

11

6

0.88

0.31–2.72

4

2

99

Other services

41

27

0.83

0.48–1.44

20

7

1.86

0.77–5.03

995

Services to buildings and dwellings

9

5

1.45

0.47–4.96

5

0

9953

Janitorial services

9

4

1.90

0.58–7.36

5

0

999

Other services, N.E.C.

19

16

0.54

0.26–1.14

7

6

0.70

0.22–2.35

Reference group: all other industries a

adjusted for age, parity, oral contraceptive use, family history, hormone therapy, partial removal of ovaries, age at menopause

123

840

Cancer Causes Control (2014) 25:829–841

control source was imposed at that time due to new privacy legislation. Although the smaller number of controls reduces the power of the study, it should not bias the results. We were also unable to assess several occupations and industries that have been implicated in previous cohort studies, such as textile, asbestos, aerospace, or printing, due to the low prevalence of such jobs among the participants in our case–control study. Overall, our study observed an EOC risk for teaching occupations, after adjusting for potential confounders. The increased risk has been observed in several previous studies although no specific characteristics of this profession have been identified as contributing factors to the disease development. If indeed women who work as teachers and in teaching-related jobs have an excess risk for EOC, a more detailed assessment of their work environment and lifestyle characteristics may be fruitful in elucidating this etiology. Acknowledgments The authors thank two anonymous reviewers for their valuable comments and suggestions which led to an improved presentation of the paper. This research was partially supported by grants from WorkSafe BC (formerly the Workers’ Compensation Board of British Columbia). We gratefully acknowledge the invaluable contribution of the research coordinators and assistants: Barbara Jamieson, Donna Kan, Zenaida Abanto, and Lynn Vo. Conflict of interest of interest.

The authors declare that they have no conflict

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Occupational exposure and ovarian cancer risk.

Relatively little work has been done concerning occupational risk factors in ovarian cancer. Although studies conducted in occupational settings have ...
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