Elevated expression of cancer/testis antigen FSIP1 in ER-positive breast tumors.

AIM: The study aimed to identify and characterize highly specific breast tumor biomarkers. METHODS: A microarray data set comprised of 513 diverse normal and tumor mRNA samples was analyzed to identify breast tumor biomarkers with minimal expression in normal tissues. RESULTS: FSIP1 was identified as a breast tumor biomarker with elevated mRNA expression in breast tumors and minimal expression in most normal tissues except the testis. Quantitative real-time PCR confirmed the elevated expression of FSIP1 mRNA in breast tumors and revealed a significant correlation with ER-positive status. Immunofluorescence staining of breast tumor sections showed that the majority of breast tumors examined in this study (20 out of 22) expressed detectable FSIP1 protein, with significantly higher than average expression in ER-positive versus ER-negative breast tumors. CONCLUSION: The prevalence and uniformity of FSIP1 expression in breast tumors, taken together with the highly restricted expression in normal tissues, suggests that FSIP1 may be an attractive target for breast cancer immunotherapy.