HORMONE REPLACEMENT TREATMENT AND BREAST-CANCER RISK - A COOPERATIVE ITALIAN STUDY

The relationship between hormone replacement treatment (HRT) and breas t cancer risk was analysed using data from a case-control study conduc ted between June 1991 and February 1994 in six Italian centres on 2569 patients aged below 75 with histologically confirmed breast cancer an d 2588 controls admitted to hospital for a wide spectrum of acute, non -neoplastic, non hormone-related diseases. Ever HRT use was reported b y 7.5% of cases and 7.5% of controls, corresponding to a multivariate odds ratio (OR) of 1.2 [95% confidence interval (CI), 0.9-1.5]. The ri sk increased with increasing duration of use: the ORs were 1.0 for use lasting less than 1 year, 1.3 for 1-4 years and 1.5 for 5 years or mo re. There was no clear pattern of risk with reference to time since st arling use, but the OR was significantly elevated (OR = 2.0, 95% CI 1. 3-2.9) for women who had stopped HRT within the last 10 years. No asso ciation was observed in those who had stopped HRT more than 10 years a go (OR = 1.0). The increased OR for women who had stopped HRT within t he last 10 years was consistent across strata of identified covariates , and was significantly related to duration of use. This study confirm s the absence of a strong association between HRT and breast cancer ri sk, although the risk estimate was above unity for women who had used HRT For 5 years or longer. However, the risk was significantly elevate d in the short to medium term after use, particularly for long-term us e, This short-term increased risk is consistent with an effect of HRT on one of the later stages of the process of breast carcinogenesis. Th e flattening of risk with increasing time since stopping, and hence th e absence of a long-term cumulative excess in breast cancer risk after stopping HRT exposure, has relevant implications on individual risk a ssessment and public health.