Breast Cancer in Lean Postmenopausal Women Might Have Specific Pathological Features

Background/Aim: The rate of obesity, an independent risk factor for breast cancer in post-menopausal women, is quite low in Japan, indicating breast cancer in lean women to be more common in the Japanese than in Westerners. However, biological characteristics of such breast cancers have not been adequately investigated. Patients and Methods: We retrospectively investigated clinicopathological breast cancer features of 566 postmenopausal Japanese women, who underwent curative surgery, in relation to patient physique based on the body mass index. Results: There were no differences in several factors examined such as tumour size according to patient physique. On the other hand, mean values of the Ki67 labelling index were significantly higher in lean compared to obese patients (p=0.027). Likewise, HER2-positive tumours were more often observed in lean patients (p=0.051). Conclusion: Lean postmenopausal women had more aggressive tumours, apparently contradicting the widely held view for breast cancer in obese women.