Uterine cancer is typically diagnosed through a tissue sample (biopsy) taken from the lining of the uterus. The process usually begins after a woman reports abnormal vaginal bleeding, which is the most common first sign. From there, a combination of imaging, physical examination, and tissue sampling confirms whether cancer is present and how far it may have spread.
Why Abnormal Bleeding Triggers the Workup
Irregular vaginal bleeding is the symptom that leads to most uterine cancer diagnoses. For postmenopausal women, any vaginal bleeding is considered abnormal and warrants evaluation. For premenopausal women, unusually heavy periods, bleeding between cycles, or spotting that doesn’t follow a normal pattern can raise concern. The good news is that bleeding tends to show up early, which is why uterine cancer is often caught before it has spread.
A pelvic exam is typically one of the first steps. Your doctor may feel for enlargement of the uterus or other abnormalities, though a physical exam alone can’t confirm or rule out cancer.
Transvaginal Ultrasound: The First Imaging Step
A transvaginal ultrasound is often the initial test used to evaluate postmenopausal bleeding. A small probe is inserted into the vagina to create images of the uterus, and one of the key measurements is the thickness of the uterine lining (the endometrium).
In postmenopausal women, a lining of 4 mm or thinner has a greater than 99% negative predictive value for endometrial cancer, meaning cancer is very unlikely at that thickness. If the lining measures thicker than 4 mm, or if the ultrasound can’t get a clear image, further testing is needed. That said, certain aggressive types of uterine cancer can occasionally develop even when the lining is less than 3 mm thick. So if bleeding persists or comes back, a tissue biopsy is recommended regardless of what the ultrasound shows.
Endometrial Biopsy: The Key Diagnostic Test
To definitively diagnose uterine cancer, a sample of the uterine lining needs to be examined under a microscope. The most common way to get that sample is an endometrial biopsy, which is usually done in a doctor’s office without general anesthesia.
During the procedure, a thin, flexible tube is passed through the cervix and into the uterus to collect a small piece of tissue. Most women describe it as feeling like strong menstrual cramps, and it typically takes only a few minutes. The tissue is then sent to a pathologist who examines the cells for signs of cancer.
An endometrial biopsy is effective at detecting endometrial carcinomas, which account for the vast majority of uterine cancers. However, it has limitations. If the biopsy doesn’t collect enough tissue, or if the results are unclear, a more thorough procedure called dilation and curettage (D&C) is the next step.
D&C and Hysteroscopy for Unclear Results
A D&C involves gently widening the cervix and using a surgical instrument to scrape tissue from the uterine lining. It collects a larger and more complete sample than an office biopsy, which makes it useful when initial results are inconclusive.
A D&C is often performed alongside a hysteroscopy, where a tiny telescope (about 1/6 inch in diameter) is inserted through the cervix into the uterus. The uterus is filled with saline to expand it, giving the doctor a direct view of the lining. This allows them to spot abnormalities like polyps or areas of unusual tissue and take targeted biopsies. Both procedures are typically done under sedation or anesthesia and are usually outpatient, meaning you go home the same day.
Why Uterine Sarcomas Are Harder to Catch
Most uterine cancers start in the lining of the uterus (endometrial carcinomas), but a small percentage start in the muscle wall. These are called uterine sarcomas, and they’re significantly harder to diagnose with standard biopsies.
The reason is straightforward: an endometrial biopsy or D&C samples the inner lining, but leiomyosarcomas (the most common type of uterine sarcoma) grow in the muscle layer beneath it. Unless the cancer has already spread from the muscle into the lining, these tests may miss it entirely. In fact, many uterine sarcomas are only diagnosed during or after surgery for what was thought to be a benign fibroid. This is one reason doctors monitor fibroids that grow rapidly or behave unusually, especially after menopause.
Staging: Determining How Far Cancer Has Spread
Once uterine cancer is confirmed by biopsy, the next priority is figuring out whether it has spread and, if so, how far. This process is called staging, and it guides treatment decisions.
MRI is the preferred imaging tool for evaluating local spread, meaning how deeply the cancer has invaded the uterine wall and whether it has reached nearby structures like the cervix. CT scans and PET/CT scans play a different role. PET/CT is particularly useful for detecting distant spread throughout the body in a single exam. It can even identify cancer in normal-sized lymph nodes as small as 5 to 9 mm that conventional CT or MRI would miss, though very tiny deposits (micrometastases) remain below the detection threshold of any current imaging.
Definitive staging often happens during surgery, when a surgeon can directly assess the uterus, surrounding tissues, and lymph nodes. Blood tests measuring a protein called CA-125 may also be checked before surgery, as elevated levels can help predict whether the cancer has spread more extensively and whether more comprehensive surgery is needed.
Molecular Testing and Genetic Screening
Modern uterine cancer diagnosis goes beyond simply identifying cancer cells. Pathologists now routinely test tumor tissue for molecular markers that reveal how the cancer is likely to behave and which treatments will work best.
The 2023 update to the international staging system (FIGO) incorporated these molecular profiles directly into how uterine cancer is classified. Tumors with a specific mutation called POLE, for instance, tend to have excellent outcomes even at more advanced stages, and patients with these tumors may not need additional treatment after surgery. Tumors with a different marker called TP53 mutation tend to be more aggressive and require more intensive treatment. Tumors with mismatch repair deficiency (dMMR), a sign that the cell’s DNA repair system isn’t working properly, respond well to a newer class of drugs called immune checkpoint inhibitors.
These molecular subtypes matter because two cancers that look identical under a microscope can behave very differently depending on their genetic profile. Testing for these markers has become a standard part of the diagnostic workup.
Lynch Syndrome Screening
Some uterine cancers are connected to an inherited condition called Lynch syndrome, which increases the risk of several cancers including uterine and colon cancer. Genetic testing for Lynch syndrome is recommended if your tumor screening results are abnormal, if you were diagnosed with uterine cancer before age 50, if you’ve had multiple types of cancer, or if several family members have had Lynch syndrome-related cancers. Identifying Lynch syndrome matters not just for your own treatment planning but also for alerting family members who may carry the same genetic risk.