Semiquantitative hormone receptor level influences response to trastuzumab-containing neoadjuvant chemotherapy in HER2-positive breast cancer

Abstract

Pathologic complete response to neoadjuvant chemotherapy without trastuzumab in hormone receptor-negative/HER2 tumors is seen in 27-45% of cases. In contrast, estrogen receptor (ER)/HER2 tumors demonstrate pathologic complete response in 8% of cases and is generally limited to weak-to-moderate ER/HER2 tumors. It is speculated that addition of trastuzumab to neoadjuvant chemotherapy regimen will increase the pathologic complete response rates in all HER2 tumors. A list of HER2 patients who received neoadjuvant chemotherapy (with trastuzumab) in the years 2007-2010 was obtained from our hospital database. The 104 HER2 tumors were classified into three groups based on semiquantitative hormone receptor and HER2 results as follows: ERBB2 (ER-/PR-H-score 10/HER2), Luminal B-HER2 Hybrid (LBHH; weak to moderate ER H-score 11-199/HER2), and Luminal A-HER2 Hybrid (LAHH; strong ERH-score 200/HER2). Pathologic complete response was defined as absence of invasive carcinoma in the resection specimen and in the lymph nodes. Percentage tumor volume reduction was also calculated based on pretherapy size and detailed evaluation of the resection specimen. In all, 52% (25 of 48 cases) of ERBB2 tumors showed pathologic complete response, which was significantly higher than the pathologic complete response rate in LBHH (33%; 10 of 30) and LAHH (8%; 2 of 26) tumors. Average percentage tumor volume reduction was also highest in ERBB2 tumors (86%), followed by LBHH (74%) and LAHH (64%) tumors. We conclude that addition of trastuzumab to neoadjuvant chemotherapy regimen significantly increases the pathologic complete response rates in all HER2 tumors. However, the benefit of trastuzumab is highest in ER-negative tumors and progressively decreases with increase in tumor ER expression. This information can be utilized to counsel patients considered for neoadjuvant chemotherapy and the same principle could be applied in the adjuvant setting. © 2011 USCAP, Inc. All rights reserved.