ORIGINAL RESEARCH * NOUVEAUTES EN RECHERCHE
Risk of breast cancer in women with breast cysts James E. Devitt,* MD, FRCSC; Teresa To,t PhD; Anthony B. Milier,: MB, FRCPC Objective: To study the occurrence of breast cancer in women with breast cysts. Design: Prospective follow-up study. Setting: Office surgical practice. Patients: All 742 women referred to the practice with breast cysts diagnosed by means of aspiration or, occasionally, biopsy between 1969 and 1985. Main outcome measures: The incidence of breast cancer and the number of years between diagnosis of breast cyst and diagnosis of cancer. The observed number of cases of breast cancer was compared with the expected number, calculated from Ontario rates of breast cancer. Results: Fifteen of the women died but did not have breast cancer. No follow-up information was available for five women. Another 38 were lost to follow-up; they did not have breast cancer at the last contact, after 2 to 17 years of follow-up. These patients were withdrawn from the study in the year in which they died or were last observed. By 1990, 34 (5%) of the women had breast cancer. The overall ratio of observed:expected cases of cancer was 3.04 (95% confidence interval 2.09 to 4.28). Breast cancer developed after 7.5 years, but the average length of follow-up was only 10.1 years. Only 3.8% of 374 women after 10 years and 5.4% of 141 women after 15 years had breast cancer. Conclusion: Women who have a gross breast cyst are at moderately increased risk of breast cancer, which usually develops only after many years.
Objectif: Etudier la survenue du cancer du sein chez les femmes atteintes de kystes mammaires. Conception: Etude de suivi prospective. Contexte: Pratique de chirurgie. Patients: La totalite des 742 femmes dirigees en chirurgie et atteintes de kystes mammaires diagnostiques au moyen de l'aspiration ou parfois de la biopsie entre 1969 et 1985.
Principales mesures des resultats: L'incidence de cancer du sein et le nombre d'annees entre le diagnostic de kyste mammaire et le diagnostic de cancer. Le nombre de cas observes de cancer du sein a ete compare au nombre prevu, a partir des taux de cancer du sein en Ontario. Resultats: Quinze femmes sont decedees, mais elles n'etaient pas atteintes d'un cancer du sein. Aucune information de suivi n'etait disponible pour cinq femmes. Trente-huit autres femmes n'ont pas ete revues; elles n'avaient pas le cancer du sein aux demieres nouvelles, apres 2 a 17 annees de suivi. Ces patientes ont et retirees de l'etude au cours de l'annee ou elles sont decedees ou lorsqu'on les a observees pour la demiere fois. En 1990, 34 (5 %) des femmes avaient eu le cancer du sein. La proportion totale de cas de cancer observes ou prevus etait de 3,04 (intervalle de confiance de 95 %, 2,09 i 4,28). Le From *the Department ofSurgery, Ottawa Civic Hospital and University of Ottawa, Ottawa, Ont., tthe National Office of the National Breast Screening Study, Toronto, and $the Department ofPreventive Medicine and Biostatistics, University of Toronto, Toronto, Ont.
Reprint requests to: Dr. James E. Devitt, Division of General Surgery, Ottawa Civic Hospital, 1053 Carling Ave., Ottawa, ON Kl Y 4E9 -
For prescribing information see page 88
CAN MED ASSOC J 1992; 147 (1)
45
cancer du sein est survenu apres 7,5 annees, mais la duree moyenne du suivi n'etait que de 10,1 annees. Apres 10 ans, seulement 3,8 % de 374 femmes et, apres 15 ans, 5,4 % de 141 femmes avaient eu le cancer du sein. Conclusion: Les femmes qui sont atteintes d'un kyste mammaire hypertrophie courent un risque moyennement eleve de cancer du sein qui ne survient habituellement qu'apres de nombreuses annees.
practice from 1969 to 1985. The cysts were diagnosed usually by means of aspiration and rarely through surgical biopsy. The age of the women at the time the first cyst was diagnosed in this practice is given in Table 1. The study was started in 1979. Follow-up information was obtained from patients referred to the office of the senior author (J.E.D.) at the time of their visit; otherwise, patients were mailed a questionnaire annually. If they failed to return the questionnaire the senior author contacted them by telephone. All of the patients were followed up until their anniversary date in 1990; this gave a minimum follow-up period of 5 years and a maximum of 21 years. In addition, but not included in the calculations, were five patients who had breast cysts and breast cancer simultaneously and five others who had breast cancer and subsequently had breast cysts. Fifteen women died but did not have breast cancer. They were withdrawn from the study in the year of their death. No follow-up information was available for five women. Another 38 were lost to follow-up; they did not have breast cancer at the last contact, after 2 to 17 years of follow-up, and were withdrawn from the study in the year in which they were last observed. Incidence rates of breast cancer by 5-year age Methods groups were derived from data published by the We included all 742 women with breast cysts Ontario Cancer Registry for 1969 to 1983."1 We then diagnosed on a referral basis in an office surgical calculated annual incidence rates by age group using
O ne or more breast cysts will develop in nearly 10% of Canadian women, usually between 35 years of age and menopause.",2 The cysts are usually diagnosed by means of aspiration in the office.'"2 They can occur before, with or after breast cancer has developed.'2 About 1% of cancers will be cystic (i.e., some sort of fluid can be aspirated from them).2 Such forms of breast cancer can easily be distinguished from simple cysts by clinical observations.",2 Follow-up studies3-10 have claimed that breast cancer is more likely to develop in patients with gross breast cysts than in other women. Unfortunately these studies had defects: small sample size3-5 or apparent selection of the subjects,6 inadequate length of follow-up,4'5'7 inadequate calculation of the expected number of cases of cancer or no description of the calculation4'5'9"0 or the age of the data.8 The purpose of this study was to observe the number of cases of breast cancer that developed in a large group of women with breast cysts. We compared the observed number with the number that could be expected in a population of women of similar age followed up for a similar period. The study is contemporary, comprehensive and Canadian.
Table 1: Distribution of women with breast cysts and those with breast cancer by age
Age at
diagnosis
of cyst, yr 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74
75-79 80-84 46
CAN MED ASSOC J 1992; 147 (1)
No. of
No. (and %) in whom cancer
patients
developed
Cumulative of women with cancer
%
1
0
0
1
0
0
7
0
0
44 110
192 227 105 29 10
6 6 2 2
0
0
(9)
9
(26) (29) (24) (6) 1 (3)
35
0
97
0
97
3 9 10 8 2
0
1 (3)
64
88 94 97
97 100
LE ler JUILLET 1992
linear interpolation for each year after entry. We estimated the expected incidence of breast cancer for each age group at each year after entry by multiplying the calculated annual incidence rate by the number of person-years for the corresponding age group. The ratio was defined as the number of observed to the number of expected cases. The 95% confidence interval (CI) was calculated according to Vandenbroucke's method.'2 The expected number of cases of breast cancer was calculated for each year
from the number of cases of breast cyst diagnosed. The overall cumulative expected number was obtained by summing the expected numbers for each study year. These calculations were made for the entire study cohort and repeated for each age group.
Results By 1990, 34 (5%) of the 742
women
had breast
Table 2: Observed number of women with breast cancer by length of time from diagnosis of cyst to diagnosis of cancer
Length of time to diagnosis of cancer, yr
No. of women with cancer
1
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 5 1 4
2 3 4 1 3 1 1 4 1
0 2
Cumulative no. (and %) of women with cancer 1 (3) 2 (6) 7 (21) 8 (24) 12 (35) 14 (41) 17 (50) 21 (62) 22 (65) 25 (74) 26 (76) 27 (79) 31 (91) 32 (94) 32 (94) 34 (100)
Table 3: Incidence of breast cancer by age at diagnosis of cyst Length of time to diagnosis of cancer, yr
Age, yr;
no. of observed
(and expected) cases of cancer
40
40-44
45-49
50-54
55-59
60
1 2 3
1 (0.1) 0 (0.1) 1 (0.1)
4
(0.1) 0(0.1) 0 (0.1) 0 (0.1) 0 (0.1) 1 (0.1) 0(0.1) 0(0.1) 0 (0.1) 0(0.1) 0 (0) 0 (0) 0 (0)
0(0.2) 0 (0.2) 1 (0.2) 1 (0.3) 0(0.3) 1 (0.2) 2 (0.2) 1 (0.2) 0 (0.2) 0(0.1) 1 (0.1) 0 (0.1) 1 (0.1) 0 (0.1)
0(0.4) (0.4) 1 (0.4) 0 (0.4) 2(0.4) 0 (0.3) 1 (0.3) 1 (0.3) 0 (0.2) 1 (0.2) 0(0.2) 1 (0.2) 3(0.2)
0(0.2) 1 (0.2) 1 (0.2) 0 (0.2) 2(0.2) 0 (0.2) 0 (0.2) 2 (0.1) 0 (0.1) 1 (0.1) 0(0.1) 0 (0.1) 0(0.1)
0(0.1) 0 (0.1) 0 (0.1) 0 (0.1) 0(0.1) 1 (0.1) 0 (0.1) 0 (0) 0 (0) 0(0)
0(0.1) 0 (0.1) 1 (0.1) 0 (0.1) 0(0.1) 0 (0.1) 0 (0) 0 (0) 0 (0) 1 (0) 0(0) 0 (0) 0(0)
0 (0.1) 0 (0.1) 0 (0) 10 (4.0)
1 (0.1) 0 (0) 0 (0)
0(0) 0 (0) 0(0) 0 (0) 0 (0) 1 (0)
0 (0) 0 (0) 0 (0)
8 (2.0)
2 (0.6)
2 (0.6)
3.26
3.13
Risk of breast cancer in women with breast cysts James E. Devitt,* MD, FRCSC; Teresa To,t PhD; Anthony B. Milier,: MB, FRCPC Objective: To study the occurrence of breast cancer in women with breast cysts. Design: Prospective follow-up study. Setting: Office surgical practice. Patients: All 742 women referred to the practice with breast cysts diagnosed by means of aspiration or, occasionally, biopsy between 1969 and 1985. Main outcome measures: The incidence of breast cancer and the number of years between diagnosis of breast cyst and diagnosis of cancer. The observed number of cases of breast cancer was compared with the expected number, calculated from Ontario rates of breast cancer. Results: Fifteen of the women died but did not have breast cancer. No follow-up information was available for five women. Another 38 were lost to follow-up; they did not have breast cancer at the last contact, after 2 to 17 years of follow-up. These patients were withdrawn from the study in the year in which they died or were last observed. By 1990, 34 (5%) of the women had breast cancer. The overall ratio of observed:expected cases of cancer was 3.04 (95% confidence interval 2.09 to 4.28). Breast cancer developed after 7.5 years, but the average length of follow-up was only 10.1 years. Only 3.8% of 374 women after 10 years and 5.4% of 141 women after 15 years had breast cancer. Conclusion: Women who have a gross breast cyst are at moderately increased risk of breast cancer, which usually develops only after many years.
Objectif: Etudier la survenue du cancer du sein chez les femmes atteintes de kystes mammaires. Conception: Etude de suivi prospective. Contexte: Pratique de chirurgie. Patients: La totalite des 742 femmes dirigees en chirurgie et atteintes de kystes mammaires diagnostiques au moyen de l'aspiration ou parfois de la biopsie entre 1969 et 1985.
Principales mesures des resultats: L'incidence de cancer du sein et le nombre d'annees entre le diagnostic de kyste mammaire et le diagnostic de cancer. Le nombre de cas observes de cancer du sein a ete compare au nombre prevu, a partir des taux de cancer du sein en Ontario. Resultats: Quinze femmes sont decedees, mais elles n'etaient pas atteintes d'un cancer du sein. Aucune information de suivi n'etait disponible pour cinq femmes. Trente-huit autres femmes n'ont pas ete revues; elles n'avaient pas le cancer du sein aux demieres nouvelles, apres 2 a 17 annees de suivi. Ces patientes ont et retirees de l'etude au cours de l'annee ou elles sont decedees ou lorsqu'on les a observees pour la demiere fois. En 1990, 34 (5 %) des femmes avaient eu le cancer du sein. La proportion totale de cas de cancer observes ou prevus etait de 3,04 (intervalle de confiance de 95 %, 2,09 i 4,28). Le From *the Department ofSurgery, Ottawa Civic Hospital and University of Ottawa, Ottawa, Ont., tthe National Office of the National Breast Screening Study, Toronto, and $the Department ofPreventive Medicine and Biostatistics, University of Toronto, Toronto, Ont.
Reprint requests to: Dr. James E. Devitt, Division of General Surgery, Ottawa Civic Hospital, 1053 Carling Ave., Ottawa, ON Kl Y 4E9 -
For prescribing information see page 88
CAN MED ASSOC J 1992; 147 (1)
45
cancer du sein est survenu apres 7,5 annees, mais la duree moyenne du suivi n'etait que de 10,1 annees. Apres 10 ans, seulement 3,8 % de 374 femmes et, apres 15 ans, 5,4 % de 141 femmes avaient eu le cancer du sein. Conclusion: Les femmes qui sont atteintes d'un kyste mammaire hypertrophie courent un risque moyennement eleve de cancer du sein qui ne survient habituellement qu'apres de nombreuses annees.
practice from 1969 to 1985. The cysts were diagnosed usually by means of aspiration and rarely through surgical biopsy. The age of the women at the time the first cyst was diagnosed in this practice is given in Table 1. The study was started in 1979. Follow-up information was obtained from patients referred to the office of the senior author (J.E.D.) at the time of their visit; otherwise, patients were mailed a questionnaire annually. If they failed to return the questionnaire the senior author contacted them by telephone. All of the patients were followed up until their anniversary date in 1990; this gave a minimum follow-up period of 5 years and a maximum of 21 years. In addition, but not included in the calculations, were five patients who had breast cysts and breast cancer simultaneously and five others who had breast cancer and subsequently had breast cysts. Fifteen women died but did not have breast cancer. They were withdrawn from the study in the year of their death. No follow-up information was available for five women. Another 38 were lost to follow-up; they did not have breast cancer at the last contact, after 2 to 17 years of follow-up, and were withdrawn from the study in the year in which they were last observed. Incidence rates of breast cancer by 5-year age Methods groups were derived from data published by the We included all 742 women with breast cysts Ontario Cancer Registry for 1969 to 1983."1 We then diagnosed on a referral basis in an office surgical calculated annual incidence rates by age group using
O ne or more breast cysts will develop in nearly 10% of Canadian women, usually between 35 years of age and menopause.",2 The cysts are usually diagnosed by means of aspiration in the office.'"2 They can occur before, with or after breast cancer has developed.'2 About 1% of cancers will be cystic (i.e., some sort of fluid can be aspirated from them).2 Such forms of breast cancer can easily be distinguished from simple cysts by clinical observations.",2 Follow-up studies3-10 have claimed that breast cancer is more likely to develop in patients with gross breast cysts than in other women. Unfortunately these studies had defects: small sample size3-5 or apparent selection of the subjects,6 inadequate length of follow-up,4'5'7 inadequate calculation of the expected number of cases of cancer or no description of the calculation4'5'9"0 or the age of the data.8 The purpose of this study was to observe the number of cases of breast cancer that developed in a large group of women with breast cysts. We compared the observed number with the number that could be expected in a population of women of similar age followed up for a similar period. The study is contemporary, comprehensive and Canadian.
Table 1: Distribution of women with breast cysts and those with breast cancer by age
Age at
diagnosis
of cyst, yr 15-19 20-24 25-29 30-34 35-39 40-44 45-49 50-54 55-59 60-64 65-69 70-74
75-79 80-84 46
CAN MED ASSOC J 1992; 147 (1)
No. of
No. (and %) in whom cancer
patients
developed
Cumulative of women with cancer
%
1
0
0
1
0
0
7
0
0
44 110
192 227 105 29 10
6 6 2 2
0
0
(9)
9
(26) (29) (24) (6) 1 (3)
35
0
97
0
97
3 9 10 8 2
0
1 (3)
64
88 94 97
97 100
LE ler JUILLET 1992
linear interpolation for each year after entry. We estimated the expected incidence of breast cancer for each age group at each year after entry by multiplying the calculated annual incidence rate by the number of person-years for the corresponding age group. The ratio was defined as the number of observed to the number of expected cases. The 95% confidence interval (CI) was calculated according to Vandenbroucke's method.'2 The expected number of cases of breast cancer was calculated for each year
from the number of cases of breast cyst diagnosed. The overall cumulative expected number was obtained by summing the expected numbers for each study year. These calculations were made for the entire study cohort and repeated for each age group.
Results By 1990, 34 (5%) of the 742
women
had breast
Table 2: Observed number of women with breast cancer by length of time from diagnosis of cyst to diagnosis of cancer
Length of time to diagnosis of cancer, yr
No. of women with cancer
1
1
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
1 5 1 4
2 3 4 1 3 1 1 4 1
0 2
Cumulative no. (and %) of women with cancer 1 (3) 2 (6) 7 (21) 8 (24) 12 (35) 14 (41) 17 (50) 21 (62) 22 (65) 25 (74) 26 (76) 27 (79) 31 (91) 32 (94) 32 (94) 34 (100)
Table 3: Incidence of breast cancer by age at diagnosis of cyst Length of time to diagnosis of cancer, yr
Age, yr;
no. of observed
(and expected) cases of cancer
40
40-44
45-49
50-54
55-59
60
1 2 3
1 (0.1) 0 (0.1) 1 (0.1)
4
(0.1) 0(0.1) 0 (0.1) 0 (0.1) 0 (0.1) 1 (0.1) 0(0.1) 0(0.1) 0 (0.1) 0(0.1) 0 (0) 0 (0) 0 (0)
0(0.2) 0 (0.2) 1 (0.2) 1 (0.3) 0(0.3) 1 (0.2) 2 (0.2) 1 (0.2) 0 (0.2) 0(0.1) 1 (0.1) 0 (0.1) 1 (0.1) 0 (0.1)
0(0.4) (0.4) 1 (0.4) 0 (0.4) 2(0.4) 0 (0.3) 1 (0.3) 1 (0.3) 0 (0.2) 1 (0.2) 0(0.2) 1 (0.2) 3(0.2)
0(0.2) 1 (0.2) 1 (0.2) 0 (0.2) 2(0.2) 0 (0.2) 0 (0.2) 2 (0.1) 0 (0.1) 1 (0.1) 0(0.1) 0 (0.1) 0(0.1)
0(0.1) 0 (0.1) 0 (0.1) 0 (0.1) 0(0.1) 1 (0.1) 0 (0.1) 0 (0) 0 (0) 0(0)
0(0.1) 0 (0.1) 1 (0.1) 0 (0.1) 0(0.1) 0 (0.1) 0 (0) 0 (0) 0 (0) 1 (0) 0(0) 0 (0) 0(0)
0 (0.1) 0 (0.1) 0 (0) 10 (4.0)
1 (0.1) 0 (0) 0 (0)
0(0) 0 (0) 0(0) 0 (0) 0 (0) 1 (0)
0 (0) 0 (0) 0 (0)
8 (2.0)
2 (0.6)
2 (0.6)
3.26
3.13
