• Norikazu Masuda, Shoichiro Ohtani, Toshimi Takano, Kenichi Inoue, Eiji Suzuki, Rikiya Nakamura, Hiroko Bando, Yoshinori Ito, Kazushige Ishida, Takashi Yamanaka, Katsumasa Kuroi, Hiroyuki Yasojima, Hiroi Kasai, Tsuyoshi Takasuka, Takaki Sakurai, Tatsuki R Kataoka, Satoshi Morita, Shinji Ohno, and Masakazu Toi.
• Department of Surgery, Breast Oncology, National Hospital Organization Osaka National Hospital, Osaka, Japan.
• Breast Cancer Res. Treat. 2020 Feb 1; 180 (1): 135-146.

PurposeThe standard of care in the neoadjuvant setting for human epidermal growth factor receptor 2 (HER2)-positive breast cancer is dual HER2-targeted therapy. However, a need to minimize treatment-related toxicity and improve pathological complete response (pCR) rates, particularly in luminal HER2-positive disease, exists.MethodsNeopeaks, a randomized, phase 2 study, compared docetaxel + carboplatin + trastuzumab + pertuzumab (TCbHP; 6 cycles; group A), TCbHP (4 cycles) followed by trastuzumab emtansine + pertuzumab (T-DM1+P; 4 cycles; group B), and T-DM1+P (4 cycles; group C) regimens in HER2-positive primary breast cancer patients; concurrent hormone therapy with T-DM1+P was administered in case of estrogen receptor positivity (ER+). Based on tumor shrinkage, nonresponders in group C were switched to 5-fluorouracil + epirubicin + cyclophosphamide (FEC; 4 cycles). Primary endpoint was pCR (comprehensive pCR ypN0 [ypT0-TisypN0]).ResultsOf 236 patients enrolled, 204 were randomized to groups A (n = 51), B (n = 52), and C (n = 101). In group C, 80 (79%) patients continued T-DM1+P following favorable response, whereas 21 (21%) nonresponders switched to FEC. pCR rate was numerically higher with the TCbHP →  T-DM1+P regimen (71%) versus the standard TCbHP (57%) and T-DM1+P (57%) regimens. The rate in group C was higher among responders continuing T-DM1+P (63%) versus nonresponders who switched to FEC (38%). pCR rates after initial 4 cycles of T-DM1+P (group C; 57%) and standard TCbHP regimen (57%) were equivalent. pCR rate in patients with ER+ was significantly higher in group B (69%) than groups A (43%) and C (51%), but was comparable in patients with ER- (67-76%). Compared with the T-DM1-based arm, the incidence of adverse events was higher in the taxane-based arms.ConclusionIn the neoadjuvant setting, the pCR rate with the standard TCbHP →  T-DM1+P regimen was numerically better than the TCbHP regimen alone and significantly better in patients with ER+. Personalization of the T-DM1+P regimen could serve as a reasonable approach to minimize toxicity while maintaining efficacy. Trial registration ID: UMIN-CTR: UMIN000014649.

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