Response to neoadjuvant chemotherapy in both the breast and lymph nodes in patients with inflammatory breast cancer.

614 Background: Optimal outcomes in Inflammatory Breast Cancer (IBC) are achieved with trimodal therapy. We sought to evaluate how differences in response to neoadjuvant chemotherapy (NAC) in the breast and axilla impact locoregional recurrence-free, distant recurrence-free and overall survival in patients with IBC. Methods: A retrospective analysis was performed on patients with IBC enrolled in a prospective registry from 2007-2025. All patients underwent NAC followed by modified radical mastectomy. Comparisons between three pathologic response groups—(A) pCR, no residual disease in breast or lymph nodes, (B) complete response in breast but not axillary nodes, and (C) complete response in axillary nodes, but not breast—were performed using Kaplan-Meier and pairwise Cox proportional hazards models. Results: 545 patients were included; median age was 50 (IQR:41-58). pCR was identified in 150 (28%) patients, while 34 (6%) were in group B, and 55 (10%) were in group C. Of patients with pCR, 6 (4%) had locoregional recurrence (LRR), compared to 6 (17%) of patients in group B, 5 (9%) of patients in group C, and 79 (25%) in patients without pCR. There was decreased risk of LRR in patients with pCR compared to no pCR, or group B (HR:0.118 CI 0.05-0.27 P<0.001; HR:0.18 CI 0.06-0.55 P=0.017). A similar decreased risk of LRR was observed in patients with group C compared to no pCR (HR:0.297 CI 0.12-0.73 P=0.01). Of patients with pCR, 31 (20%) had distant recurrence, compared to 14 (41%) of patients in group B, 23 (41%) of patients in group C, and 183 (60%) in patients who did not have pCR. There was decreased risk of distant recurrence in patients with pCR compared to no pCR, or patients in group C (HR0.25 CI 0.17-0.37 P<0.0001; HR0.43 CI0.25-0.74 P=0.007). There was also a decreased risk of distant recurrence in patients with group C compared to no pCR (HR0.59 CI 0.38-0.91 P=0.027). Mean OS was longer in patients with pCR compared to partial response or no pCR (12.4 vs 7.95 years). The risk of death was lower in patients with pCR compared to partial or no pCR, as well as those with group C compared to no pCR. Conclusions: In patients with IBC, the lowest risk for recurrence was achieved with pCR. However, even with pCR, there was still a 20% chance of distant recurrence. Partial response through clearance of the lymph node disease provided some reduction in risk of recurrence compared to no pCR.