Single-Cell Analysis Reveals Adipose Cancer-Associated Fibroblasts Linked to Trastuzumab Resistance in Human Epidermal Growth Factor Receptor 2-Positive Breast Cancer

Trastuzumab, a first-line targeted agent for HER-2-positive breast cancer, often faces challenges due to resistance. The IGF-1R/IRS-1/AKT pathway hyperactivation has been linked to this resistance, but the primary culprit, whether epithelial cells or cancer-associated fibroblasts (CAFs), remains uncertain. To investigate, we employed seRNA-seq to differentiate CAFs and epithelial cells in trastuzumab-sensitive and resistant breast cancer samples. iTALK analysis revealed potential interactions between CAFs and epithelial cells through IGF-1. We then analyzed 43 HER-2-positive breast cancer samples treated with trastuzumab, confirming higher expression of IGF-1R/IRS-1/AKT pathway proteins using immunohistochemistry. Notably, we identified five CAFs subtypes with varying proportions in both trastuzumab-sensitive and resistant samples. Further analysis revealed elevated IGF-1 levels in CAFs of trastuzumab-resistant tissues, particularly in adipose CAFs. Immunohistochemistry staining corroborated overexpression of COL11A1 (an adipose CAF marker) and increased IGF-1R and Tyr-phosphorylated IRS-1 in HER-2-positive breast cancer, associated with poor trastuzumab response. Our findings suggest that CAFs, particularly adipose CAFs, may induce trastuzumab resistance in HER2-positive breast cancer epithelial cells through IGF-1-mediated activation of the IGF-1R/IRS-1/AKT pathway.