Women affected by gross cystic disease of the breast have an increased risk of breast cancer. We report here the incidence of breast cancer by cyst type and intracystic epidermal growth factor (EGF) concentration. Our retrospective study included 504 women who had at least 1 cyst aspiration between 1985 and 1993. Cyst fluids were processed for electrolyte concentration (n = 378), EGF concentration (n = 347) or both (n = 337). Age-standardized incidence ratios (SIRs) were estimated using the population of the Genoa Cancer Registry. A multivariate Poisson regression model was used to estimate relative risks (RRs) when the study groups were compared directly. By June 1999, 19 invasive breast cancers had developed in the cohort of women. The age SIR of breast cancer calculated for the whole cohort was 3.32 (95% confidence interval 2.00-5.18). The ratio was not affected by age and was only moderately increased in women with a positive family history of breast cancer and type I cysts (i.e., those with a Na+/K+ ratio <3). However, it was significantly increased in women with high EGF concentrations. Direct comparisons confirmed that age, cyst type and family history only moderately increased the RR, whereas EGF concentration was a strong predictor of risk. Our results confirm that women affected by palpable cysts have an increased risk of developing breast cancer and suggest that the risk is higher in women with high intracystic EGF concentrations.
Copyright 2001 Wiley-Liss, Inc.