Which of the following is considered a tumor marker for breast cancer?

CA 15-3 is a well-established tumor marker specifically associated with breast cancer. It is a mucin-like glycoprotein that is released into the bloodstream by breast cancer cells, and elevated levels can indicate the presence of breast cancer or monitor treatment response and disease recurrence. While CA 15-3 is not used for initial diagnosis, it serves as a useful tool in tracking the progression of the disease in diagnosed patients.

Troponin is primarily a marker for myocardial infarction and is used in cardiology to assess heart damage, making it irrelevant for breast cancer diagnosis or monitoring. PSA (prostate-specific antigen) is a marker primarily used for prostate cancer, not breast cancer, and glucose levels are more associated with metabolic conditions like diabetes rather than cancer-specific monitoring. Therefore, CA 15-3 stands out as the appropriate tumor marker for breast cancer in this context.