Survival outcomes of Black/African American (B/AA) patients with HER2-negative (IHC 0, 1+, 2+ and ISH-), advanced breast cancer (HER2-neg aBC) across three academic cancer centers in the United States.

129 Background: As B/AA patients are underrepresented in clinical research, data is limited on survival outcomes of B/AA patients with HER2-neg aBC. This study compared survival outcomes of these patients against those of non-B/AA patients. Methods: This was a retrospective cohort study at Huntsman Cancer Institute, H. Lee Moffitt Cancer Centre and Research Institute, and Winthrop P. Rockefeller Cancer Institute. Adult patients diagnosed with HER2-neg aBC from 2010 to 2021 were eligible. Patient data were extracted via chart review, including self-reported race from clinical records. HER2-low status was defined as immunohistochemistry (IHC) scores 1+ or 2+ and negative fluorescence in situ hybridization test; HER2-neg comprised HER2-low and IHC 0. Overall survival (OS), i.e. time until death, and progression-free survival (PFS), i.e. time until death or disease progression, were estimated using Kaplan-Meier methods with treatment start as index date and censoring at date of last follow-up or 12/31/2021, whichever earlier. Association between B/AA race and survival was evaluated using multivariable Cox regression. Results: A total of 869 patients were HER2-neg, 95 were B/AA, and 64 (67%) were HER2-low while 31 (33%) had IHC 0 disease. Compared to non-B/AA patients (85% non-Hispanic White), fewer B/AA patients had stage IV disease (38% vs 57%, p=0.001), lobular histology (3% vs 14%, p=0.001) and positive hormone receptor status (HR) (60% vs 78%, p<0.001). B/AA patients showed shorter median OS and PFS than non-B/AA patients overall and in subgroups defined by stage and HR but 95% confidence intervals (CI) overlapped (Table). Controlling for stage and HR, B/AA patients had shorter OS (Hazards ratio: 1.4, 95% CI: 1.0-1.9) but no difference in PFS (Hazards ratio: 1.2, 95% CI: 0.9-1.6). Conclusions: OS of B/AA patients with HER2-neg aBC was shorter than that of non-B/AA patients controlling for staging and HR. A sizable proportion of B/AA patients have HER2-low disease and more studies are needed to confirm if this patient population has different outcomes compared to non-B/AA. Survival outcomes of B/AA patients vs non-B/AA patients. Overall Survival (months) Progression-free Survival (months) B/AA Non-B/AA B/AA Non-B/AA n Mdn (95% CI) n Mdn (95% CI) n Mdn (95% CI) n Mdn (95% CI) Overall 95 41.4 (28.3 to 69.4) 774 56.7 (50.0 to 66.2) 95 9.9 (8.0 to 20.3) 773 16.1 (13.9 to 18.3) Staging IIIB/IIIC 60 69.4 (39.1 to NR) 339 NR (110.1 to NR) 60 10.2 (8.0 to 23.8) 339 22.5 (15.0 to 37.8) IV 35 28.1 (18.2 to 40.9) 435 39.4 (35.5 to 44.0) 35 9.6 (7.3 to 25.7) 434 13.9 (11.6 to 17.0) Hormone receptor Positive 57 41.4 (27.8 to 69.4) 609 62.0 (55.1 to 69.7) 57 8.6 (7.8 to 20.3) 609 17.1 (14.1 to 19.7) Negative 38 40.9 (23.1 to NR) 162 41.6 (24.2 to 68.3) 38 10.2 (7.7 to NR) 161 11.8 (9.3 to 17.2) B/AA – Black/African American, Mdn – median, NR – not reached.