HER2 cluster amplification as a factor of an especial sensitivity for anti-HER2 neoadjuvant therapy with biosimilar of trastuzumab in Russian women with breast cancer stage II-III.

Abstract

e12102 Background: Effect of neoadjuvant chemotherapy (NACT) is extremely important for patients with HER2-positive breast cancer stage II-III as it correlates with long-term outcomes. However, predictive factors for achieving complete pathologic response (pCR) remain unclear. Aim of the study: Assess an impact of clinical, morphological and genetic factors on pCR achievement in patients with HER2-positive breast cancer stage II-III treated by biosimilar of trastuzumab. Methods: We studied treatment results in 73 patients with HER2-positive breast cancer (BC) stage II-III (aged 29-71, median – 51 years), treated with NACT with anti-HER2 therapy and radical surgery in “N.N. Blokhin National Medical Research Center of Oncology” оf the Ministry of Health of the Russian Federation in 2015-2018. After radical surgery pathologic response was assessed. Initially operable tumors were observed in 45,2% patients, locally advanced - in 53,4%. Luminal HER2-positive BC was diagnosed in 41,1%, non-luminal HER2-positive in 58,9%. Ki67 was high (≥ 20%) in 91,5%. NACT included anthracycline and non-antracycline regimens with addition of biosimilar of trastuzumab ± pertuzumab. Radical mastectomy was performed in 78,8% patients, 21,2% had breast-conserving surgery. We studied biopsies obtained before the start of treatment in all women, HER2 amplification was detected by HER2 IQFISH pharmDx (DAKO) kit in accordance with ASCO/CAP 2018 guidelines. In 87,1% HER2+ status was defined as ASCO/CAP 2018 category 1; cluster amplification was detected in 30,1% patients. We analyzed the rate of bpCR и tpCR achievement depending on clinical, pathological data and amplification of HER2. Results: Pathologic complete response in primary tumor (bpCR) was achieved in 57,4%, both in primary tumor and lymph nodes (tpCR) – in 48,9% patients; bpCR achievement depended on age, NACT regimen, addition of pertuzumab and HER2 copy number ( < 0,05). The highest rate of bpCR was noted in women aged 50 and older (71,9%, p = 0,026); in patients received TCH±Р regimen (80,0%, p = 0,045); with addition of pertuzumab (88,9%, p = 0,049); and if cluster amplification was detected (81%, p = 0,013). Cluster amplification was the only one significant predictive factor for achieving tpCR: with cluster amplification - 68,8%, without - 38,7% (p = 0,049). Conclusions: Cluster amplification of HER2 is the most significant factor of especial sensitivity for NACT with biosimilar of trastuzumab in HER2-positive BC stage II-III.