Clinicogenomic Characterization of Inflammatory Breast Cancer

Inflammatory breast cancer (IBC) is a rare and clinically distinct form of breast cancer associated with poor outcomes. The biological mechanisms driving IBC remain poorly understood, partly due to limited large-scale genomic studies that directly compare IBC with non-IBC cases.

We conducted a retrospective analysis of 140 patients with IBC (68 primary tumors and 72 metastatic tumors) and 2,317 patients with non-IBC (700 primary tumors, 65 local recurrences, and 1,552 metastases). We compared clinicopathologic features, single-nucleotide variants, copy-number variants, tumor mutational burden, and exploratory survival outcomes between IBC and non-IBC tumors.

The most frequent somatic alterations in IBC were detected in TP53 (72%), ERBB2 (32%), PIK3CA (24%), CCND1 (12%), MYC (9%), FGFR1 (8%), and GATA3 (8%). Multivariate logistic regression revealed a significant enrichment of TP53 single-nucleotide variants in IBC, particularly in HER2+ and hormone receptor-positive disease. Tumor mutational burden did not differ between IBC and non-IBC cases. In HER2+ disease, a pathway analysis revealed an enrichment of NOTCH pathway alterations. TP53, CCND1, and RB1 alterations were associated with poor outcomes in IBC.

This study provides a comprehensive resource of somatic alterations in a large cohort of patients with metastatic IBC and non-IBC, highlighting genomic features associated with worse outcomes. Our findings reveal a significant enrichment of TP53 mutations, reinforcing its critical role in IBC pathogenesis. Few other distinct differences in IBC were observed, suggesting further investigations-beyond bulk sequencing of the somatic genome-are required to better understand the biology driving this aggressive disease.