CA – 125 is specific marker of:
**Core Concept**
CA-125 is a tumor-associated antigen that is primarily used as a marker for ovarian cancer. It is a mucin-type glycoprotein that is overexpressed on the surface of many epithelial ovarian cancer cells. Elevated levels of CA-125 can also be found in other conditions, such as endometriosis, pelvic inflammatory disease, and benign ovarian cysts.
**Why the Correct Answer is Right**
CA-125 is specific for ovarian cancer due to its overexpression on the surface of epithelial ovarian cancer cells. This overexpression is thought to be due to the abnormal expression of the MUC16 gene, which encodes the CA-125 protein. While CA-125 can be elevated in other conditions, it is not specific for these conditions and can be used as a marker for ovarian cancer in conjunction with other diagnostic tools.
**Why Each Wrong Option is Incorrect**
**Option A:** While CA-125 can be elevated in breast cancer, it is not a specific marker for this condition. Breast cancer is often associated with other biomarkers, such as estrogen receptor and HER2 status.
**Option B:** CA-125 is not a marker for lung cancer. Lung cancer is often associated with other biomarkers, such as cytokeratin 7 and 20.
**Option C:** CA-125 is not a marker for colorectal cancer. Colorectal cancer is often associated with other biomarkers, such as carcinoembryonic antigen (CEA).
**Clinical Pearl / High-Yield Fact**
CA-125 levels can be elevated in patients with benign conditions, such as endometriosis and pelvic inflammatory disease. Therefore, a diagnosis of ovarian cancer should not be based solely on elevated CA-125 levels, but rather on a combination of clinical and radiological findings.
**Correct Answer:** C.