What are the two types of uterine cancer?

Uterine cancers can be of two types: endometrial cancer, which is common, and uterine sarcoma, which is rare.

The split comes down to which layer of the uterus the cancer starts in. The uterus is a hollow organ shaped like a pear. Its inner lining is called the endometrium. Before menopause, that lining thickens and sheds each month. The thick middle wall is muscle, called the myometrium. Endometrial cancer starts in the lining. Uterine sarcoma starts in the muscle or the tissue that supports it.

That is not a small point. The two act differently, are found at different times, and are treated with different drugs.

Endometrial cancer

This is the large group. Uterine cancer is the most common cancer of the female reproductive organs in the US. The American Cancer Society expects about 68,270 new cases in 2026. Nearly all of them are endometrial.

It usually shows itself early. The main warning sign is vaginal bleeding or discharge that is not a period. Any bleeding after menopause counts. That sign is hard to ignore, so 67% of uterine cancers are found while still inside the uterus. At that stage, 5-year relative survival is 94.9% for women diagnosed from 2016 through 2022.

Most cases trace back to years of estrogen that is not balanced by progesterone. NCI lists these risk factors: obesity, metabolic syndrome, type 2 diabetes, estrogen-only hormone therapy, and tamoxifen taken for breast cancer. Lynch syndrome, which runs in families, also raises the risk sharply.

Stages run from I through IV. Stage I splits into IA and IB. The split depends on how deeply the tumor has grown into the muscle wall. That depth helps decide whether radiation or chemotherapy is added after surgery.

Uterine sarcoma

Sarcomas are only 2% to 5% of uterine cancers. NCI sorts them into these groups:

• Carcinosarcoma, 40% to 50% of sarcoma cases
• Leiomyosarcoma, about 30%
• Endometrial stromal sarcoma, about 15%
• Adenosarcoma and other rare forms

Sarcomas tend to be found later. They also grow faster. For a leiomyosarcoma still inside the uterus, 5-year survival is about 50%. For all other stages it drops to 0% to 20%.

The causes are mostly unknown. NCI notes one proven factor in 10% to 25% of cases. That factor is past pelvic radiation, often given 5 to 25 years earlier. Sometimes it was given for a bleeding problem that was not cancer. Tamoxifen raises the risk of sarcoma too.

Why the distinction affects your care

A sarcoma is often not spotted before surgery. Fibroids are muscle growths that are not cancer. On a scan, a fibroid and a leiomyosarcoma can look alike. That is why surgeons avoid power morcellation when cancer has not been ruled out. Morcellation cuts a growth into pieces inside the body. If the growth is a hidden sarcoma, that can spread tumor cells through the belly.

Endometrial cancer is different. It is usually found before surgery, through an office biopsy of the lining or a procedure called dilation and curettage.

If you have been told you have uterine cancer, ask which of the two types it is. Ask for the subtype as well. Ask whether the tumor was tested for mismatch repair deficiency, sometimes reported as MSI-high. That result can open the door to immunotherapy. It can also flag Lynch syndrome in your family. And if you have bleeding after menopause with no diagnosis yet, get it checked soon rather than watched.