Utility of folate receptor alpha immunohistochemistry in cytology specimens of metastatic breast carcinoma, metastatic serous carcinoma of Müllerian origin, and primary lung adenocarcinoma.

BACKGROUND: Folate receptor alpha (FRA) overexpression by immunohistochemistry (IHC) has been shown to various degrees in histologic specimens from breast ductal carcinoma (DC), serous carcinoma of Müllerian origin (SCM), and primary lung adenocarcinoma (ADC) among others. Antifolate therapies have recently shown usefulness in FRA overexpressing malignancies. We assessed the feasibility for detecting FRA overexpression by IHC in cytologic cell blocks (CB) from the aforementioned carcinomas.

METHOD: Cases of breast DC, SCM and lung ADC were included. The CB were immunostained with FRA employing mAb 26B.3.F2 (Biocare Medical, Concord, CA). FRA staining was scored qualitatively, by intensity, and staining area.

RESULTS: 4/20 (20%) triple negative breast cancer (TNBC), 27/29 (93%) SCM, and 20/22 (91%) lung ADC showed positive FRA immunoreactivity. All ER/PR positive (n = 5) and Her2-neu positive (n = 5) DC were negative with FRA IHC.

CONCLUSIONS: FRA expression can be detected with a higher degree of confidence in SCM (93%) and lung ADC (91%) in CB, and to a lesser degree in TNBC. Our data also shows that FRA expression by IHC was more frequently associated with TNBC (20%) when compared with ER/PR positive or Her2neu positive breast cancers. FRA overexpression detected by IHC in CB is highly concordant with the published results of surgical specimens from SCM and lung ADC and less so from TNBC. Hence, IHC FRA analysis can be performed in the CB preparation with a high degree of confidence in SCM and lung ADC.