Retrospective Analysis of HER2+ Breast Cancer Outcomes at a County Hospital: Do Published Outcomes Hold up in the Real World?

Introduction: Landmark trials repeatedly demonstrate that pertuzumab and trastuzumab plus standard chemotherapy have the best outcomes in human epidermal growth factor receptor 2 (HER2) positive breast cancer in the neoadjuvant, adjuvant, and metastatic setting. However, many of these multicenter landmark trials lack diversity and studied largely Caucasian populations. Our goal is to address this under-representation of minorities, and compare pathologic complete response (pCR) rates in our predominantly Hispanic population with HER2 positive breast cancer receiving the same neoadjuvant chemotherapy (NACT) at Olive View-UCLA Medical Center (OVMC) to that of pCR rates observed in the TRYPHAENA trial.Methods: For this retrospective cohort study, we compiled a list of 53 patients aged 18 and older, 52 female and 1 male, with HER2 positive breast cancer identified by fluorescence in situ hybridization treated at OVMC from December 2015 to May 2018. Our population was 57% Hispanic, 13% white, 13% Filipino, 11% Asian, 2% black, and 4% other. The complete list included patients receiving standard neoadjuvant, adjuvant, and metastatic chemotherapy regimens. We analyzed 23 female patients with HER2 positive breast cancer staged I to IIIC, receiving standard NACT (docetaxel, carboplatin, trastuzumab, and pertuzumab). Metastatic HER2 positive breast cancer patients were excluded. The primary outcome studied was pCR rates after receiving NACT. pCR was defined as the absence of invasive cancer cells from tissue samples removed after surgery. Secondary outcomes measured were side effects of chemotherapy. pCR rates and side effects were compared to TRYPHAENA. Data regarding insurance status, breast cancer detection modality, and time to seek medical attention were recorded.Results: 50% of our patients who received NACT achieved pCR. Our pCR rates mirrored those observed in the TRYPHAENA trial (51.9%). The most common side effect observed in our population was diarrhea. A higher proportion (37.5%) of our patients had liver function test (LFT) elevation compared to the TRYPHAENA trial (3.9%). Baseline LFTs were normal prior to treatment in 96% of patients. In terms of modality of detection, 70% were self-palpated, 26% were detected through routine mammography, and 4% were found incidentally. Average time from mass discovery to seeking medical attention was 3.4 months. Only 26% had medical insurance at diagnosis. Although not included in our study, 28% of our patients were