CA125 is used for?
**Core Concept**
CA125 is a tumor marker used in the monitoring and follow-up of patients with epithelial ovarian cancer. It is a mucin-type glycoprotein that is overexpressed on the surface of ovarian cancer cells. Elevated levels of CA125 can indicate recurrence or progression of the disease.
**Why the Correct Answer is Right**
CA125 is used as a tumor marker because it is often elevated in the serum of patients with epithelial ovarian cancer. The CA125 antigen is a mucin-type glycoprotein that is attached to the surface of cancer cells through a mucin-type glycosylphosphatidylinositol (GPI) anchor. The levels of CA125 in the serum can be measured using an enzyme-linked immunosorbent assay (ELISA) or other techniques. An elevated level of CA125 can indicate a poor prognosis, and serial measurements can be used to monitor the response of the tumor to treatment.
**Why Each Wrong Option is Incorrect**
**Option A:** CA125 is not used for the diagnosis of breast cancer. While breast cancer patients may have elevated levels of CA125, this marker is not specific for breast cancer and can be elevated in a variety of other conditions.
**Option B:** CA125 is not used for the monitoring of lung cancer. While some lung cancer patients may have elevated levels of CA125, this marker is not specific for lung cancer and can be elevated in a variety of other conditions.
**Option C:** CA125 is not used for the screening of ovarian cancer. While CA125 is used to monitor patients with known ovarian cancer, it is not sensitive or specific enough to be used as a screening test for the general population.
**Clinical Pearl / High-Yield Fact**
A normal CA125 level does not rule out ovarian cancer, as some patients with early-stage disease may have normal levels. Conversely, an elevated CA125 level does not necessarily indicate ovarian cancer, as it can be elevated in a variety of other conditions.
**Correct Answer:** C.