CA 15-3: A tumor marker most useful in following the course of treatment in women diagnosed with breast cancer, especially advanced breast cancer. CA 15-3 levels are rarely elevated in women with early stage breast cancer.
Cancers of the ovary, lung, and prostate may also raise CA 15-3 levels. Elevated levels of CA 15-3 may be associated with noncancerous conditions, such as benign breast or ovarian disease, endometriosis, pelvic inflammatory disease, and hepatitis. Pregnancy and lactation can also cause CA 15-3 levels to rise.