Morphologic features do not influence response to trastuzumab-containing neoadjuvant chemotherapy in HER2-positive breast cancer.

Trastuzumab-containing neoadjuvant chemotherapy in patients with HER2-positive breast cancer is highly effective in reducing tumor volume and enables more patients to have breast-conserving surgery. The tumor hormone receptor level has been shown to significantly influence response to trastuzumab-containing neoadjuvant chemotherapy. In this study, we comprehensively evaluated various morphologic features and proliferative activity in 50 HER2-positive invasive breast carcinomas treated with trastuzumab-containing neoadjuvant chemotherapy to determine whether any of these features have the same predictive value as tumor hormone receptor content. The tumor proliferation activity as measured by Ki-67 and various morphologic parameters were compared between tumors that achieved >50% tumor volume reduction including pathologic complete response (pCR) and tumors that showed 50% tumor volume reduction. Thirty-seven cases (74%) showed >50% tumor volume reduction including 18 cases with pCR. Thirteen cases (26%) showed 50% tumor volume reduction. Neither morphologic variables nor Ki-67 labeling index were predictive of >50% tumor volume reduction. In contrast, hormone receptor status and semiquantitative H scores for hormone receptors were predictive of>50% tumor volume reduction. The mean estrogen and progesterone receptor H scores for tumors that showed >50% tumor volume reduction (including pCR) were 77 (median 10) and 31 (median 0), respectively, compared with 168 (median 200) and 79 (median 75) for cases that showed 50% tumor volume reduction. Semiquantitative scoring for hormone receptors provides useful information in terms of therapeutic response in HER2-positive tumors.