It is derived from MUC1.[4] CA 15-3 and associated CA 27-29 are different epitopes on the same protein antigen product of the breast cancer-associated MUC1 gene.
Elevated CA15-3, in conjunction with alkaline phosphatase (ALP), was found to be associated with an increased chance of early recurrence in breast cancer.[5]
Both CA 15-3 and CA 27-29 may be elevated in patients with benign ovarian cysts, benign breast disease, and benign liver disease. Elevations may also be seen in cirrhosis, sarcoidosis and lupus.
^Bearz A, Talamini R, Vaccher E, et al. (2007). "MUC-1 (CA 15-3 antigen) as a highly reliable predictor of response to EGFR inhibitors in patients with bronchioloalveolar carcinoma: an experience on 26 patients". Int. J. Biol. Markers. 22 (4): 307–11. doi:10.1177/172460080702200411. PMID18161663.