STn and Prognosis in Breast Cancer

Sialyl-Tn (STn) is a carbohydrate antigen formed by the premature 2-6 sialylation of N-acetylgalactosamine. It belongs to a family of antigens widely expressed in carcinomas but only to a limited degree in normal tissue. The expression of STn has been associated with prognosis in different tumors. In this immunohistochemical study of 218 patients with invasive stage I-III breast cancer, STn was expressed in 39% of the tumors. High expression of STn correlated with estrogen and progesterone hormone receptor negativity (p = 0.0002 and p = 0.0003, respectively), and marginally with large tumor size (p = 0.04), high S-phase fraction (p = 0.04) and aneuploidy (p = 0.04), but not significantly with node status, grade or age. The patients had a median follow-up of 17 years. The breast-cancer-specific survival rate of patients with STn-negative cancers was higher than that of patients with cancers that expressed STn during the first 5 years of the follow-up (p = 0.013), but the difference between the groups decreased during the long-term follow-up. STn expression seems to be a marker for short-term, but not for long-term breast cancer outcome prediction.