Prognosis of Japanese Breast Cancer Based on Hormone Receptor and HER2 Expression Determined by Immunohistochemical Staining

BACKGROUND: We classified Japanese breast cancer patients based on estrogen receptor (ER), progesterone receptor (PR), and HER2 protein expression and compared their prognoses. METHODS: We compared the background and prognostic factors of 600 patients with breast cancer who were assigned to the following groups: luminal A (ER + and/or PR + and HER2-; n = 431; 71.8%), luminal B (ER + and/or PR + and HER2 + ; n = 27; 4.5%), HER2 (ER-, PR-, and HER2 + ; n = 39; 6.5%) and basal-like (BBC; ER-, PR-, and HER2-; n = 103; 17.2%). RESULTS: Background factors did not significantly differ among the groups. Disease-free survival rates were significantly lower for the luminal B, HER2, and BBC subtypes than for the luminal A subtype. Cancer tended to recur earlier and overall survival was significantly lower for the BBC than for the luminal A and HER2 subtypes. Overall survival rates for the luminal B, HER2, and luminal A subtypes were comparable. CONCLUSIONS: The subtype distribution for Japanese and Caucasian patients was comparable. The prognosis for the BBC subtype was poorest among all subtypes. Breast cancer tended to recur earlier for the luminal B and HER2 subtypes than for the luminal A subtype; however, overall survival did not significantly differ among them.