FOLR1 and peritoneum cancer: This immunohistochemical test utilizes a mouse monoclonal anti-FOLR1 antibody (clone FOLR1-2.1) to detect folate receptor alpha (FOLR1) protein expression in formalin-fixed, paraffin-embedded (FFPE) tissue specimens from epithelial ovarian, fallopian tube, or primary peritoneal cancers [14].