COMT and breast cancer: Third, there were significant differences on genotypes about COMT (rs165599 and rs737865) between HER− and HER+ groups; the A/A carriers of COMT rs165599 and the G/G and A/G carriers of COMT rs737865 performed more poorly than COMT (G/G, A/A, respectively) carriers on tests of TBPM in breast cancer patients with HER2−, and the COMT polymorphism may be an underlying genetic factor for the enhancement of the venture to chemotherapy-related PM impairment in breast cancer patients with disparate status of HER2.