Long term effects of tamoxifen: Biological Effects of Tamoxifen Working Party

Abstract A total of 153 breast cancer patients who participated in two trials of adjuvant tamoxifen and who had not recurred were recruited into a study of the long term effects of tamoxifen. There were 60 controls (no tamoxifen), 73 ex-users (mostly for 2 years) and 20 current users (median treatment duration 72 months) and the median follow-up time was 7 years. A wide ranging study of lipids, hormones, bone density and haemostasis was undertaken. When compared with controls, current users had lower cholesterol levels (especially low density cholesterol), and increased triglyceride levels. Thyroid hormones were higher and sex hormone binding globulin was almost doubled. Bone density was non-significantly higher, clotting times were slightly shorter and fibrinogen and antithrombin III levels were reduced. However few of these changes persisted in ex-users, suggesting that most of the biological effects of treatment are reversible on cessation of treatment. This is reassuring for potentially negative side-effects, but also indicates that potentially positive ‘side-effects’ such as cholesterol lowering only occur while on active treatment.