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.

DESIGN

Cohort study of women with breast cysts aspirated between 1983 and 1993 who were followed up until December 1994 for occurrence of breast cancer.

SETTING

Major cancer prevention centre.

SUBJECTS: 802 women with aspirated breast cysts.

MAIN OUTCOME MEASURES: Type of breast cyst based on cationic content of cyst fluid: type I (potassium:sodium ratio > 1.5), type II (potassium:sodium ratio < 1.5), or mixed (both types). 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 with breast cysts seems to be concentrated among women with type I breast cysts.