Abstract P5-08-39: Low risk of contralateral breast cancer rates in Asian women- A case for not recommending contralateral prophylactic mastectomy

Abstract

Abstract Introduction The rates of contralateral prophylactic mastectomy (CPM)appears to be higher in the west as compared to the east.1,2There is a suggestion of an improved survival benefit of CPM. 1The trends are increasing in the west and little is known in Asia. In western data a rate of 0.5 to 1% per year is often quoted. However, There is scarcity of epidemiological data on rates of contralateral breast cancer (CBC) in Asia. Known predictors of CBC in the west include high stage at diagnosis, early age at diagnosis, presence of family history, genetic predisposition, time from first diagnosis and hormone receptor status. Little is known in Asia. Population based registries are not available in Malaysia as in many Southeast Asian countries. This study aims to provide CBC rates to provide evidence for informed decision making of CPM in Asians. Method A prospective database of newly diagnosed Stage I and II breastcancer patients diagnosed in University Malaya Medical Centre between 1993 to 2012 were analysed. Data on CBC were obtained from institutional database and medical records. Multivariate analysis used Cox regression was applied to observe for any associations with multiple variables such as age at diagnosis, time from diagnosis, presence of family history, menopausal status, ethnic groups, parity and hormone status. Results A total of 3060 Stage I and II patients were prospectively followed up. 127 (4.2%) women developed contralateral breast cancer.At 5 years, 57 (1.9%) and at 10 years, 100(3.4%) developed CBC. Using a multivariate model, the only independent predictor of developing contralateral breast cancer at 5 years was a positive family history OR 1.97(CI 1.02-3.80). However, at 10 years we found the effect of positive family history diminished OR1.57 (CI 0.94-2.64) and younger women were more likely to develop cancer, those aged 51 to 64 years OR 0.29 (CI 0.11-0.73) , >65 years OR 0.20 (CI 0.07-0.60)compared to those less than 35 years. The other factors in the model were not significant. Discussion There is an increasing rate of CPM at 22% from 9% in the west1. A study in Singapore showed a low CPM rate of 1.25%2 . Although uptake of CPM in Asia has not been reported extensively and appears low, the trends may rise and that evidence is needed to counsel patients on the benefits and harms of CPM if patients request for CPM. Given the lower incidence of breast cancer in Malaysia ie 5% average risk compared to 10% in the west, an urgent need to document the risk of contralateral breast cancer, and this data from a single institution is the first to report this rates in Southeast Asia. Conclusion The data shows that risk of contralateral breast cancer is low in this Southeast Asian country. Any recommendations or practice of CPM should be dealt with extreme caution.