Lower FGFR2 mRNA Expression and Higher Levels of FGFR2 IIIc in HER2-Positive Breast Cancer

Fibroblast growth factor receptor 2 (FGFR2) has been associated with breast cancer. We performed in silico analyses to investigate the <i>FGFR2</i> mRNA expression and splice variants associated with breast cancer subtypes. Online databases, including cBioPortal and TCGA SpliceSeq, were used to examine the association between the <i>FGFR2</i> expression and splice variants with breast cancer subtypes. A higher <i>FGFR2</i> mRNA was significantly associated with luminal, oestrogen receptor (ER)-positive breast cancers, and invasive lobular carcinomas, whereas a lower <i>FGFR2</i> was associated with human epidermal growth factor receptor 2 (HER2)-positive breast cancer and invasive ductal carcinomas. The epithelial alternatively spliced <i>FGFR2 IIIb</i> isoform was significantly enriched in ER+ breast cancer, while the mesenchymal <i>FGFR2 IIIc</i> isoform was significantly prevalent in HER2+ cancer. Increased levels of <i>FGFR2</i> and <i>IIIb</i> splice isoforms are associated with less aggressive breast cancer phenotypes, while decreased levels of <i>FGFR2</i> and increased <i>IIIc</i> splice isoform are associated with more aggressive phenotypes.