International Journal of Epidemiology O Oxford University Press 1977
Vol. 6, No. 4 Printed in Great Britain
Risk Factors of Breast Cancer in Finland IRMASOINI1
INTRODUCTION
Much emphasis has been placed on identifying individuals who have a high risk of breast cancer especially in high-incidence areas. In an international collaborative study (1, 2) no significant difference was found in the epidemiological characteristics of breast cancer between high- and low-risk areas. Finland represents an area of intermediate breast cancer incidence (40*1/100,000 in 1973) (3), which is low compared with the other Nordic countries (4). The incidence curve by age (5) follows that of high-risk areas and continues to rise after menopause (Figure 1). Even though the incidence of breast cancer in Finland is well documented by different demographic characteristics (5) there is no report on the association of risk factors (reproductive, hormonal, familial and others) with the risk of breast cancer in Finnish women.
Incidence per 10s 160140-
120-
10080-
60-
20-
60
MATERIAL AND METHODS
The series consists of the breast cancer cases aged 41-60 (95 patients) treated at the Department of Radiotherapy of Tampere Central Hospital, Finland, from 1970 to 1975. The controls (534 women) originate from a breast cancer screening programme in 1974 to 1975 for females aged 41-60 in Tampere (6). The controls were selected by taking a subject following a case with an abnormal finding and with no referral in the mass screening programme. The cases diagnosed for breast cancer in 1 Detection Centre and Laboratories of the Pirkanmaa Cancer Society, and Department of Public Health, University of Tampere, Tampere, Finland
365
T" 70 60 Age (years)'
Fro. 1 Cancer of the breast in Finland: mean annual age-specific incidence rates in 1956-1960, 1961-1965 and 1966-1970, females.
connection with this screening (27 patients) were added to the total number of cases. The cases and controls were interviewed in order to obtain epidemiological data concerning reproductive, hormonal and other characteristics associated with the risk of breast cancer. The interviewers were one of five specially trained nurses or a physician (IS) and remained the same throughout
Downloaded from http://ije.oxfordjournals.org/ at University of Auckland on March 26, 2015
Soini, I (Detection Centre and Laboratories of the Pirkanmaa Cancer Society and Department of Public Hearth, University of Tampere, Tampere, Finland) Risk factors of breast cancer in Finland. International Journal of Epidemiology, 1977, 6 : 365-373. The risk of breast cancer in Finland is low (40-1/100,000) compared with the other Nordic countries. A casecontrol study was carried out on 122 cases of breast cancer and 534 controls between the ages of 41 and 60. It was found that age at first marriage and birth of the first child as well as the number of abortions and parity adjusted for age at first birth were associated with the breast cancer risk, whereas lactation was not The results did not confirm the hypothesis (de Waard) that overweight and/or the size of the woman influence the risk of breast cancer.
366
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
Reproductive and hormonal characteristics
The risk of breast cancer for single women in terms of unit risk for women who had ever been married was one in the present series. Mean age at first marriage for the cases and controls was 22 • 1 and 21-0, and at first birth 26-3 and 25-3 years. The risk of breast cancer for women entering their first marriage at the age of 25 years or older was twice that of women who married under the age of 20 years (Figure 2). The relative risk of breast cancer for women having their first child at the age of 30 years or older was 1 -9 in terms of unit risk for women with their first birth under the age of 25 years (Figure 3). The total number of births also had an effect on cancer risk (Figure 4) but only in women over 50 years of age (Table II). RBARVE RISK 2J0 2JO-
where Xn is the number of cases
RR =
with a selected characteristic, Xn the number of controls with the same characteristic, Xu and Xa the numbers of cases and controls without this characteristic. Confidence intervals for the relative risks were estimated using the method proposed by Gart (8).
1515
10 •
RESULTS
The total series consisted of 122 cases and 534 controls. The proportion of menopausal women was essentially the same in both of the groups (Table I).
as
TABLE!
Cases and controls by age Age (years) 41-50 51-60 Total
Cases
Controls
Total
62 60
280 254
342 314
122
534
656
Vol. 6, No. 4 Printed in Great Britain
Risk Factors of Breast Cancer in Finland IRMASOINI1
INTRODUCTION
Much emphasis has been placed on identifying individuals who have a high risk of breast cancer especially in high-incidence areas. In an international collaborative study (1, 2) no significant difference was found in the epidemiological characteristics of breast cancer between high- and low-risk areas. Finland represents an area of intermediate breast cancer incidence (40*1/100,000 in 1973) (3), which is low compared with the other Nordic countries (4). The incidence curve by age (5) follows that of high-risk areas and continues to rise after menopause (Figure 1). Even though the incidence of breast cancer in Finland is well documented by different demographic characteristics (5) there is no report on the association of risk factors (reproductive, hormonal, familial and others) with the risk of breast cancer in Finnish women.
Incidence per 10s 160140-
120-
10080-
60-
20-
60
MATERIAL AND METHODS
The series consists of the breast cancer cases aged 41-60 (95 patients) treated at the Department of Radiotherapy of Tampere Central Hospital, Finland, from 1970 to 1975. The controls (534 women) originate from a breast cancer screening programme in 1974 to 1975 for females aged 41-60 in Tampere (6). The controls were selected by taking a subject following a case with an abnormal finding and with no referral in the mass screening programme. The cases diagnosed for breast cancer in 1 Detection Centre and Laboratories of the Pirkanmaa Cancer Society, and Department of Public Health, University of Tampere, Tampere, Finland
365
T" 70 60 Age (years)'
Fro. 1 Cancer of the breast in Finland: mean annual age-specific incidence rates in 1956-1960, 1961-1965 and 1966-1970, females.
connection with this screening (27 patients) were added to the total number of cases. The cases and controls were interviewed in order to obtain epidemiological data concerning reproductive, hormonal and other characteristics associated with the risk of breast cancer. The interviewers were one of five specially trained nurses or a physician (IS) and remained the same throughout
Downloaded from http://ije.oxfordjournals.org/ at University of Auckland on March 26, 2015
Soini, I (Detection Centre and Laboratories of the Pirkanmaa Cancer Society and Department of Public Hearth, University of Tampere, Tampere, Finland) Risk factors of breast cancer in Finland. International Journal of Epidemiology, 1977, 6 : 365-373. The risk of breast cancer in Finland is low (40-1/100,000) compared with the other Nordic countries. A casecontrol study was carried out on 122 cases of breast cancer and 534 controls between the ages of 41 and 60. It was found that age at first marriage and birth of the first child as well as the number of abortions and parity adjusted for age at first birth were associated with the breast cancer risk, whereas lactation was not The results did not confirm the hypothesis (de Waard) that overweight and/or the size of the woman influence the risk of breast cancer.
366
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
Reproductive and hormonal characteristics
The risk of breast cancer for single women in terms of unit risk for women who had ever been married was one in the present series. Mean age at first marriage for the cases and controls was 22 • 1 and 21-0, and at first birth 26-3 and 25-3 years. The risk of breast cancer for women entering their first marriage at the age of 25 years or older was twice that of women who married under the age of 20 years (Figure 2). The relative risk of breast cancer for women having their first child at the age of 30 years or older was 1 -9 in terms of unit risk for women with their first birth under the age of 25 years (Figure 3). The total number of births also had an effect on cancer risk (Figure 4) but only in women over 50 years of age (Table II). RBARVE RISK 2J0 2JO-
where Xn is the number of cases
RR =
with a selected characteristic, Xn the number of controls with the same characteristic, Xu and Xa the numbers of cases and controls without this characteristic. Confidence intervals for the relative risks were estimated using the method proposed by Gart (8).
1515
10 •
RESULTS
The total series consisted of 122 cases and 534 controls. The proportion of menopausal women was essentially the same in both of the groups (Table I).
as
TABLE!
Cases and controls by age Age (years) 41-50 51-60 Total
Cases
Controls
Total
62 60
280 254
342 314
122
534
656
