ObjectiveThe aim of this study was to quantify the expression of melanoma-antigen family A proteins (MAGE-A) and New York esophageal squamous cell carcinoma-1 (NY-ESO-1) in breast cancer and establish the prognosis of breast cancer patients with MAGE-A and NY-ESO-1 co-expression.MethodsA total of 122 patients with breast cancer were recruited for this study. Their clinicopathological data were collected retrospectively, and the MAGE-A and NY-ESO-1 expressions in paraffin-embedded specimens from the 122 patients were evaluated using immunohistochemical analysis. In addition, the survival states of the patients were recorded.ResultsFifty-four patients (44.26%) were MAGE-A positive and 46 (37.70%) were NY-ESO-1 positive. Interestingly, 22 of the 46 NY-ESO-1-positive cases co-expressed MAGE-A. The expression of MAGE-A was positively associated with estrogen-receptor status (χ2 = 4.026, p = 0.045) and human epidermal growth factor receptor 2 status (χ2 = 5.482, p = 0.019), while the expression of NY-ESO-1 was positively associated with p53 expression (χ2 = 4.541, p = 0.033). Of the 122 patients, the lowest survival rate was observed in patients with NY-ESO-1 (+)/MAGE-A (+), with a 5-year survival rate of 59.09% and a median survival of 97 months.ConclusionThe results showed that MAGE-A and NY-ESO-1 were frequently expressed in breast cancer patients. The co-expression of MAGE-A and NY-ESO-1 occurred in about 18% of these patients, and it may indicate a poor prognosis.