Survival and Treatment Patterns in Stage III Inflammatory and Noninflammatory Breast Cancer

Importance: Inflammatory breast cancer (IBC) is an aggressive form of cancer for which trimodality therapy (TMT) is standard, but TMT use may be decreasing. Survival outcomes between patients with IBC and non-IBC by tumor subtype are unclear, and survival trends over time have not been reported. Objective: To compare breast cancer (BC)-specific survival (BCSS) and overall survival (OS) between IBC and non-IBC by tumor subtype, and to examine trends in TMT use and survival over time. Design, Setting, and Participants: This cohort study used population-based data from the Surveillance, Epidemiology, and End Results program. Patients with stage III BC diagnosed between 2010 and 2020 were categorized as having IBC (T4d) and non-IBC. TMT included neoadjuvant systemic therapy, mastectomy, dissection of more than 5 axillary nodes, and adjuvant radiation. Data analysis was conducted from January to October 2024. Exposure: Diagnosis of IBC and receipt of TMT. Main Outcomes and Measures: BCSS and OS between IBC and non-IBC were evaluated stratified by tumor subtype. Multivariable Cox models were used to estimate adjusted hazard ratios (aHRs) across subtypes and to assess trends in BCSS and OS over time. Results: Among 47 702 patients with stage III BC (3227 with IBC [6.8%] and 44 475 with non-IBC [93.2%]), the median (IQR) age at diagnosis was 57 (47-68) years, and 47 215 (99.0%) were women. Across all tumor subtypes, IBC was associated with worse BCSS compared with non-IBC, including hormone receptor-positive, ERBB2-negative disease (aHR, 1.53; 95% CI, 1.37-1.70) and triple-negative BC (aHR, 1.69; 95% CI, 1.50-1.89). Among patients with IBC, TMT receipt was associated with better BCSS compared with no TMT (aHR, 0.67; 95% CI, 0.59-0.77). From 2010 to 2020, use of TMT among patients with IBC decreased from 33.9% (111 of 327 patients) to 24.2% (52 of 215 patients), and no significant improvement in BCSS or OS over time was observed, whereas survival improved among patients with non-IBC. Conclusions and Relevance: In this cohort study of stage III BC, IBC was associated with worse BCSS and OS than stage III non-IBC across all tumor subtypes. TMT use in IBC was low and decreased significantly over time. BCSS and OS did not improve over time for patients with IBC treated with TMT, whereas BCSS and OS improved for those with non-IBC.