COHORT STUDY OF ASSOCIATION OF RISK OF BREAST-CANCER WITH CYST TYPE IN WOMEN WITH GROSS CYSTIC-DISEASE OF THE BREAST

Objective: To assess correlation between type of breast cyst and risk of breast cancer in women with gross cystic disease of the breast. Des ign: Cohort study of women with breast cysts aspirated between 1983 an d 1993 who were followed up until December 1994 for occurrence of brea st cancer. Setting: Major cancer prevention centre. Subjects: 802 wome n with aspirated breast cysts. Main outcome measures: Type of breast c yst based on cationic content of cyst fluid: type I (potassium:sodium ratio > 1.5), type II (potassium:sodium ratio < 1.5), or mixed (both t ypes). Subsequent occurrence and type of breast cancer.Results: After median follow up of six years (range 2-12 years) 15 cases of invasive breast cancer and two ductal carcinomas in situ were diagnosed in the cohort: 12 invasive cancers (and two carcinomas in situ) among the 417 women with type I cysts, two cancers among the 325 women with type II cysts, and one among the 60 women with mixed cysts. The incidence of breast cancer in women with type I cysts was significantly higher than that in women with type II cysts (relative risk 4.62 (95% confidence interval 1.26 to 29.7)). These results were confirmed after adjustment for several risk factors for breast cancer (relative risk 4.24 (1.12 to 27.5)). Conclusions: The increased risk of breast cancer of women w ith breast cysts seems to be concentrated among women with type I brea st cysts.