C4A and breast cancer: To delve deeper into our investigation of upregulated genes containing Ig domains as potential novel immunotherapy biomarkers in metastatic breast cancer cells, our analysis revealed a diverse array of genes, including SORCS2, C4A, PSG5, SIRPA, LRIG1, CSF2RA, MDGA1, CRLF2, IL1R1, SORL1, PDGFRB, and IL7R.