Background: Although inflammatory breast cancer (IBC) is postulated to be a distinct biological entity, practice guidelines and previous data suggest that treatment and outcomes are influenced by standard approximated biological subtype. The aim of this study was validation in a large recent National Cancer Database (NCDB) patient cohort. Methods: Patients with non-metastatic IBC treated in 2010–2015 with neoadjuvant systemic therapy and surgery were identified from the NCDB. Approximated biological subtypes were categorized as oestrogen receptor-positive (ER+)/human epidermal growth factor receptor 2-negative (HER2−), ER−/HER2− and HER2+. Total pathological complete response (pCR) was defined as ypT0/ypTis, ypN0. χ2 tests were used to compare pCR rates, and Kaplan–Meier curves and Cox proportional hazards regression to analyse overall survival. Results: Among 4068 patients with IBC (median age 56 years), the approximated biological subtype was ER+/HER2− in 1575 (38·7 per cent), HER2+ in 1323 (32·5 per cent) and ER−/HER2− in 1170 (28·8 per cent). A total of 3351 patients (84·0 per cent) were cN+ at presentation, with no differences across subtypes. Total pCR rates varied significantly by subtype: ER+/HER2− (6·2 per cent), HER2+ (38·8 per cent), ER−/HER2− (19·1 per cent) (P < 0·001), as did breast pCR rates (10·4, 44·5 and 25·2 per cent respectively) and nodal pCR rates (16·9, 56·9 and 33·1 per cent). The 5-year overall survival rate varied significantly across subtypes (ER+/HER2− 64·9 per cent, HER2+ 74·0 per cent, ER−/HER2− 44·0 per cent; P < 0·001) and by pCR within subtypes (all P < 0·001). In multivariable analysis, ER−/HER2− subtype (hazard ratio 2·89 versus HER2+ as reference; P < 0·001) and absence of total pCR (hazard ratio 3·23; P < 0·001) predicted worse survival. Conclusion: Both treatment response and survival in patients with IBC varied with approximated biological subtype, as among other invasive breast cancers. These data support continued tailoring of systemic treatment to approximated biological subtype and highlight the recent improved outcomes in patients with HER2+ disease.
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