Molecular Characterization and Classification of HER2-Positive Breast Cancer Inform Tailored Therapeutic Strategies.

HER2-positive breast cancer is an aggressive subtype that accounts for 15-20% of all breast cancers. Recent studies have suggested that HER2-positive breast cancer is a group of heterogeneous diseases with different sensitivities to standard treatment regimens. Revealing the molecular heterogeneity of HER2-positive breast cancer could potentially enable more precise treatment strategies. Here, we performed multiomics profiling on a HER2-positive breast cancer cohort and identified four transcriptome-based subtypes. The classical HER2 (HER2-CLA) subtype comprised 28.3% of the samples and displayed high ERBB2 activation and significant benefit from anti-HER2 therapy. The immunomodulatory (HER2-IM) subtype (20%) featured an immune-activated microenvironment, potentially suitable for de-escalated treatment and immunotherapy. The luminal-like (HER2-LUM) subtype (30.6%) possessed similar molecular features of hormone receptor-positive HER2-negative breast cancer, suggesting endocrine therapy and CDK4/6 inhibitors as a potential therapeutic strategy. Lastly, the basal/mesenchymal-like (HER2-BM) subtype (21.1%), had a poor response to current anti-HER2 dual-targeted therapies and could potentially benefit from tyrosine kinase inhibitors. The molecular characteristics and clinical features of the subtypes were further explored across multiple cohorts, and the feasibility of the proposed treatment strategies was validated in patient-derived organoid and patient-derived tumor fragment models. This study elucidates the molecular heterogeneity of HER2-positive breast cancer and paves the way for a more tailored treatment.

Molecular features and clinical implications of the heterogeneity in Chinese patients with HER2-low breast cancer.

The molecular heterogeneity and distinct features of HER2-low breast cancers, particularly in the Chinese population, are not well understood, limiting its precise management in the era of antibody‒drug conjugates. To address this issue, we established a cohort of 434 Chinese patients with HER2-low breast cancer (433 female and one male) and integrated genomic, transcriptomic, proteomic, and metabolomic profiling data. In this cohort, HER2-low tumors are more distinguished from HER2-0 tumors in the hormone receptor-negative subgroup. Within HER2-low tumors, significant interpatient heterogeneity also exists in the hormone receptor-negative subgroup: basal-like tumors resemble HER2-0 disease, and non-basal-like HER2-low tumors mimic HER2-positive disease. These non-basal-like HER2-low tumors are enriched in the HER2-enriched subtype and the luminal androgen receptor subtype and feature PIK3CA mutation, FGFR4/PTK6/ERBB4 overexpression and lipid metabolism activation. Among hormone receptor-positive tumors, HER2-low tumors show less loss/deletion in 17q peaks than HER2-0 tumors. In this work, we reveal the heterogeneity of HER2-low breast cancers and emphasize the need for more precise stratification regarding hormone receptor status and molecular subtype.