Clinical characteristics of patients with no evidence of disease (NED) versus residual disease (RES) to anti-HER2 therapy in metastatic breast cancer (MBC): A multi-institutional analysis.

Zachary William Neil Veitch Princess Margaret Cancer Centre, Toronto, ON, Canada info_outline Zachary William Neil Veitch, Philippe L. Bedard, Patricia A. Tang, Jessica L. Conway, Domen Ribnikar, Hamzeh Albaba, Karen M. King, Sasha M. Lupichuk, David W. Cescon

Authors Zachary William Neil Veitch Princess Margaret Cancer Centre, Toronto, ON, Canada info_outline Zachary William Neil Veitch, Philippe L. Bedard, Patricia A. Tang, Jessica L. Conway, Domen Ribnikar, Hamzeh Albaba, Karen M. King, Sasha M. Lupichuk, David W. Cescon Organizations Princess Margaret Cancer Centre, Toronto, ON, Canada, Tom Baker Cancer Centre, University of Calgary, Calgary, AB, Canada, Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada, Cross Cancer Institute, Edmonton, AB, Canada, Tom Baker Cancer Centre, Calgary, AB, Canada, Princess Margaret Cancer Centre, University of Toronto, Toronto, ON, Canada Abstract Disclosures Research Funding Other Background: Anti-HER2 therapy has improved survival in HER2+ MBC. Yet, large patient cohorts with no evidence of disease (NED) with long-term follow up are incompletely described in the literature. We evaluated the clinical characteristics of patients with HER2+ MBC and prolonged response to anti-HER2 therapy, exhibiting NED vs Residual disease (RES). Methods: Patients treated with chemotherapy plus trastuzumab (CT) from 2005-2013, or taxane plus trastuzumab-pertuzumab (TTP), or trastuzumab-emtansine (TDM1) from 2012-2016 for HER2+ MBC at Princess Margaret Cancer Centre in Toronto, Ontario or in Alberta, Canada were included. Duration on anti-HER2 therapy (without switch) was collected. Patients with median duration of response (MDR; months) 2x higher than phase II/III trials for each regimen (CT = 18.2; TTP = 40.4; TDM1 = 25.2) were included to select for prolonged response. Clinical features (ie: stage at diagnosis, survival, etc) and oncologist/radiologist reported best response were collected. Responses were grouped as NED (including sclerotic bone metastases) or RES. Clinical variables were evaluated by Chi-square and survival by Kaplan-Meier (log-rank). Results: 2403 patients (CT = 1830; TTP = 394; TDM1 = 179) were evaluated. After cut-off, 119 patients (5%) were included, with NED in 41% (49/119) and RES in 59% (70/119). More women aged < 50 vs ≥50 (p = 0.015) had NED (61%) than RES (39%). No breast surgery (curative or metastatic) showed higher (p = 0.015) rates of NED (49%) relative to RES (27%). More women having NED (92%) than RES (37%) were still alive (p < 0.0001) at data cut-off, with improved mPFS (years; p < 0.0001) for NED (11.2, 95%CI: 11.2-NR) vs RES (3.0, 2.7-3.6), and mOS (years; p < 0.0001) for NED (NR) vs RES (3.4, 95%CI: 2.8-4.2). Significance persisted with TDM1 patients excluded. Treatment type (p = 0.053) and number of organs with metastases (p = 0.067) were of borderline significance. Conclusions: Patients with NED have improved survival compared to RES. Younger age and avoiding breast surgery correlates with NED. Evaluation of genomic factors influencing NED are planned.