A protein found on certain epithelial cells, which line the inside and outside surfaces of the body. It may be found in higher than normal amounts in patients with some types of cancer, including breast, ovarian, lung, and prostate cancers, or in other conditions. Measuring the amount of MUC-1 in the blood may help to find out how well cancer treatment is working or if cancer has come back. MUC-1 is a type of tumor marker.