CA-125 can be elevated in uterine (endometrial) cancer, but it is not a reliable screening test for detecting it. With a sensitivity of only about 53%, the test misses roughly half of endometrial cancers. It performs better as a tool for gauging how advanced a known cancer may be, rather than for finding one in the first place.
What CA-125 Actually Measures
CA-125 is a protein shed into the bloodstream by a large molecule called MUC16, which sits on the surface of cells lining the uterus, ovaries, and other organs. When those cells become cancerous or inflamed, they can produce more of this protein, pushing blood levels higher. The standard threshold is 35 units per milliliter. Anything above that is generally considered elevated.
The protein is most commonly associated with ovarian cancer, where it has been used for decades. But because the uterine lining also produces it, endometrial tumors can raise CA-125 levels too, especially when the cancer has grown deep into the uterine wall or spread to lymph nodes.
How Accurate Is It for Uterine Cancer?
Not very, if the goal is early detection. In a study comparing women with endometrial cancer to those with abnormal uterine bleeding but no cancer, CA-125 had a sensitivity of 52.63% and a specificity of 80% at a cutoff of 17.8 U/mL. That means it correctly flagged just over half of the women who actually had cancer, and it correctly cleared 80% of those who did not. A test that misses nearly half of true cases is not dependable for screening.
For comparison, the standard cutoff of 35 U/mL that labs typically use is even less sensitive for endometrial cancer, since many early-stage tumors produce only modest amounts of the protein. A normal CA-125 result does not rule out uterine cancer.
Where CA-125 Is More Useful: Staging and Prognosis
CA-125 becomes considerably more informative once uterine cancer has already been diagnosed. Doctors often draw it before surgery to help estimate how far the disease may have spread. A study published in Scientific Reports found that women with CA-125 levels at or above 222 U/mL had a 67% greater risk of having stage III or IV disease compared to those with lower levels. At that same threshold, the risk of lymph node metastasis nearly doubled (a 98% increase in risk), and the risk of cancer invading blood and lymph vessels rose by 39%.
In practical terms, a very high preoperative CA-125 can alert a surgical team that a cancer is likely more advanced than imaging alone might suggest. That information can influence the extent of surgery and whether lymph nodes are removed for evaluation. It does not replace imaging or surgical findings, but it adds a useful data point to the overall picture.
Many Non-Cancer Conditions Raise CA-125
One of the biggest limitations of CA-125 is that plenty of benign conditions push it above 35 U/mL. Endometriosis, uterine fibroids, pelvic inflammatory disease, and pancreatitis can all elevate levels, sometimes as high as 200 U/mL. Even the follicular phase of the menstrual cycle, early pregnancy, liver diseases like hepatitis and cirrhosis, and pericarditis can cause a spike.
This means an elevated result in a woman who has not been diagnosed with cancer could easily reflect something other than malignancy. Without additional testing, the number alone tells you very little.
How Uterine Cancer Is Actually Diagnosed
The gold standard for diagnosing endometrial cancer is an endometrial biopsy. A thin, flexible tube is inserted through the cervix to collect a small tissue sample from the uterine lining. The procedure is done in a doctor’s office, takes a few minutes, and can cause cramping, mild bleeding, and rarely infection or uterine perforation. Several biopsy devices exist (the Pipelle is the most common), and in about 36% of cases the sample may not contain enough tissue for a clear diagnosis, requiring a repeat procedure or a dilation and curettage (D&C) under sedation.
Transvaginal ultrasound is often the first step when a woman reports abnormal bleeding. It measures the thickness of the uterine lining. Among postmenopausal women who turn out to have endometrial cancer, 96% will show an endometrial thickness greater than 6 mm on ultrasound. However, ultrasound alone has a sensitivity of only about 63% and a specificity around 60% for cancer, so an abnormal result almost always needs to be followed up with a biopsy.
Most endometrial cancers (about 85%) are caught at an early stage because the disease tends to cause noticeable symptoms, particularly abnormal vaginal bleeding. That early detection through symptoms is a major reason survival rates for uterine cancer are relatively high compared to ovarian cancer, where symptoms often appear late.
Should You Ask for a CA-125 Test?
If you have no symptoms and no known cancer, a CA-125 test is unlikely to help and could easily lead to unnecessary worry or follow-up procedures over a result that turns out to be benign. No major medical organization recommends routine CA-125 screening for endometrial cancer in the general population.
If you have already been diagnosed with uterine cancer, your oncologist may order CA-125 before surgery to help assess the likely extent of disease. Some doctors also use it after treatment to watch for signs of recurrence, though its role in post-treatment monitoring is less well established than in ovarian cancer. A rising CA-125 after treatment can be an early signal that cancer has returned, but it is not definitive on its own and would prompt imaging or biopsy for confirmation.
For women at high genetic risk of endometrial cancer, such as those with Lynch syndrome, guidelines focus on annual transvaginal ultrasound and endometrial biopsy starting in the mid-30s rather than blood marker testing.