Multiple Cancer/Testis Antigens Are Preferentially Expressed in Hormone-Receptor Negative and High-Grade Breast Cancers

Background: Cancer/testis (CT) antigens are protein antigens normally expressed only in germ cells of testis, and yet are expressed in a proportion of a wide variety of human cancers. CT antigens can elicit spontaneous immune responses in cancer patients with CT-positive cancers, and CT antigen-based therapeutic cancer vaccine trials are ongoing for "CT-rich" tumors. Although some previous studies found breast cancer to be "CT-poor", our recent analysis identified increased CT mRNA transcripts in the ER-negative subset of breast cancer. Methodology/Principal Findings: In this study, we performed a comprehensive immunohistochemical study to investigate the protein expression of eight CT genes in 454 invasive ductal carcinomas, including 225 ER/PR/HER2-negative (triple-negative) carcinomas. We found significantly more frequent expression of all eight CT antigens in ER-negative cancers, and five of them-MAGEA, CT7, NY-ESO-1, CT10 and CT45, were expressed in 12-24% of ER-negative cancers, versus 2-6% of ER-positive cancers (p < 0.001 to 0.003). In comparison, GAGE, SAGE1 and NXF2 were only expressed in 3-5% of ER-negative and 0-2% of ER-positive cancers. ER-negative cancers were also more likely to simultaneously co-express multiple CT antigens, with 27% (34/125) of ER-negative, CT-positive tumors expressing three or more CT antigens. HER2 status had no consistent effect on CT expression, and triple-negative carcinomas showed similar frequencies of MAGEA and NY-ESO-1 expression as ER-negative/HER2-positive carcinomas. More frequent CT expression was also found in tumors with higher nuclear grade (p < 0.001 to p = 0.01) and larger in size (> 2 cm). Conclusions/Significance: CT antigens are preferentially expressed in hormone receptor-negative and high-grade breast cancer. Considering the limited treatment options for ER/PR/HER2 triple-negative breast cancer, the potential of CT-based immunotherapy should be explored.