CA-125 is a marker antigen for the screening of the following malignancy:
**Core Concept**
The **CA-125** antigen is a high-molecular-weight glycoprotein expressed on the surface of certain cells, particularly those of **ovarian** origin. It is utilized as a tumor marker in the monitoring and follow-up of patients with **ovarian cancer**. The expression of CA-125 is not exclusive to ovarian cancer but is also found in other types of cancers and benign conditions.
**Why the Correct Answer is Right**
CA-125 is primarily used as a marker for **ovarian cancer**, especially for monitoring response to treatment and detecting recurrence. Elevated levels of CA-125 can be found in the serum of patients with ovarian cancer, particularly those with **epithelial ovarian cancers**, which account for about 90% of ovarian cancers. The mechanism involves the shedding of CA-125 from the surface of ovarian cancer cells into the bloodstream.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because while CA-125 can be elevated in other cancers, it is not the primary marker for them.
**Option B:** Incorrect as it is not the most specific marker for the mentioned condition.
**Option C:** Incorrect because, although CA-125 can be elevated in some cases, it's not the primary marker used for this condition.
**Clinical Pearl / High-Yield Fact**
It's crucial to remember that CA-125 is not specific to ovarian cancer and can be elevated in various benign conditions, such as **endometriosis**, **pregnancy**, and **pelvic inflammatory disease**, making it less useful as a screening tool in the general population but valuable for monitoring disease recurrence in patients with known ovarian cancer.
**Correct Answer:** D. Ovarian cancer.