Cohort study of association of risk of breast cancer with cyst type in women with gross cystic disease of the breast

Abstract 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