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Breast

E83: Locoregional Therapy for Inflammatory Breast Cancer: How Much is Enough?

Introduction: Inflammatory breast cancer (IBC) is a rare breast cancer subtype with historically poor outcomes. For non-metastatic IBC patients, excellent locoregional (LR) control has been reported following trimodality therapy with aggressive LR treatment including resection of all involved skin at presentation and twice daily radiotherapy (RT) for young patients and for those who do not achieve a pCR. We evaluated survival outcomes in a contemporary cohort of IBC patients treated with a standardized, less intensive LR therapy protocol.

Methods: We retrospectively identified 225 stage III IBC patients treated with neoadjuvant chemotherapy (NAC), modified radical mastectomy (MRM), and RT from 1/2006-12/2022 at a single institution. Routinely, a conventional MRM including excision of residually involved skin post-NAC with wide margins and flat closure was performed. RT included 50 Gy in 18-25 daily fractions to the chest wall and regional nodes plus a skin bolus. We calculated the crude rate of isolated locoregional recurrence (LRR) and estimated disease-free survival (DFS) using Kaplan-Meier survival curves and a Cox proportional hazard regression model.

Results: Median follow-up was 3.6 years (interquartile range 1.8, 6.3 years). Cohort characteristics are shown in the Table. Isolated LRR was observed in 2.2% (5/225) patients at a median of 11.4 months (IQR 9.8, 14.1 months). There were no LRR events among patients who achieved a pCR. Distant metastasis occurred in 29.8% (67/225) patients and 54 deaths were recorded. Overall, 3-year DFS was 70% (95% CI, 63%, 76%). For patients with triple negative (TN) disease, 3-year DFS was 52% (95% CI, 35%, 67%) vs. other subtypes (HR+/HER2+: 79% [95% CI, 62%, 89%]; HR-/HER2+: 75% [95% CI, 61%, 85%]; HR+/HER2-: 70% [95% CI, 58%, 79%]; p< 0.001). 3-year DFS was 64% (95% CI, 55%, 71%) in patients without pCR vs. 84% (95% CI, 72%, 91%) for those with pCR (p< 0.001). On multivariable analysis, TN subtype (HR 2.31, 95% CI, 1.15, 4.66, p=0.019), ypN2 disease (HR 3.06, 95% CI, 1.35, 6.93, p=0.007) and ypN3 disease (HR 4.03, 95% CI, 1.80, 9.00) were the only factors associated with worse DFS. Subgroup analysis demonstrated worse DFS among TN patients without pCR vs. other subtypes without pCR (p< 0.001) and no difference in DFS between subtypes in patients with pCR (p=0.42).

Conclusions: Safely limiting the extent of IBC-specific LR therapy is feasible, evidenced by low rates of isolated LRR at 3.6-year median follow-up. Worse survival among TN patients with higher residual nodal burdens underscores the need for novel systemic therapies for IBC.

Learning Objectives:

  • Describe the rate of isolated locoregional recurrence in patients with inflammatory breast cancer treated with trimodality therapy including once daily radiotherapy for all patients, independent of risk factors.
  • Describe disease-free survival in patients with inflammatory breast cancer treated with trimodality therapy including once daily radiotherapy for all patients, independent of risk factors.
  • List predictors of disease-free survival in patients with inflammatory breast cancer.