Abstract
Patients with HER2(+) early breast cancer (EBC) receiving neoadjuvant systemic therapy (NAST) have poorer outcomes if they have residual disease (RD). We analyzed IDFS and brain metastasis (BM) rates in patients with HER2(+) EBC treated with NAST and report the outcomes of patients with HER2(-) RD. Patients with HER2(+) EBC who received NAST between 1 Jan 2019 and 31 Jan 2022 were reviewed. IDFS was defined as the time from surgery until first occurrence of invasive breast cancer recurrence, distant recurrence, or death from any cause. The total cohort was 594 patients. pCR (ypT0/isN0) was achieved in 325(55%) and RD was seen in 269(45%) patients. In 269 patients with RD, 45(17%) did not have HER2 retesting and were excluded. In the remaining 224 patients, 143(64%) were HER2(+) and 81(36%) were HER2(-). With a median follow up of 24 months, 8 patients developed BM at initial recurrence, 4/325(1.2%) with pCR and 4/143(2.8%) with HER2(+) RD. IDFS events occurred in 22/594(3%) patients; 14/269(5%) in RD and 8/325(2%) in pCR (p = 0.04). There was no difference in IDFS between 9/143(6%) patients with HER2(+) RD or 5/81(6%) with HER2(-) RD (p = 0.10). Patients with RD had higher IDFS events than those with pCR. In those with RD, 36% lost HER2(+) status; IDFS events appeared similar in those with HER2(+) RD versus those with HER2(-) RD. The BM events seen in those with RD and pCR highlights the need for more effective therapy in NAST and adjuvant setting to minimize BM risk.