The uterus is pear shaped with the narrow end pointing down. This narrow lower end, which extends into the vagina, is the cervix. The wider upper part is the body of the uterus, or the uterine corpus.
There are three layers to the body of the uterus:
- Endometrium, the inner lining
- Myometrium, a thick layer of muscle
- Serosa, the outer covering, or membrane
Connective tissue called stroma supports the other uterine tissues.
Most cancer in the uterus—more than 95 percent—starts in the endometrium. This is called endometrial cancer or endometrial carcinoma. (“Carcinoma” is the term for cancer that starts in one of the body’s linings or membranes.) We discuss endometrial cancer in its own section of the website.
In rare cases, cancer starts in another tissue of the uterus. Most of these cancers are uterine sarcoma. (“Sarcoma” is the term for cancer that starts not in a body lining but in one of the body’s other tissues, like muscle, bone, fat, or fibrous tissue.) Only about 3% of uterine cancers are uterine sarcoma. Other less common uterine cancers are uterine papillary serous carcinoma, clear cell carcinoma, and carcinosarcoma (also called malignant mixed mesodermal tumors or malignant mixed mullerian tumors).
Uterine sarcoma occurs when cells in the body of the uterus, usually in the muscle layer, begin to grow abnormally. These cells do not respond to regular cell growth, division, and death signals like they are supposed to. They also don’t organize normally. Instead they grow into a tumor, which may break through into other layers of the uterus.
Although the cervix is part of the uterus, cancer that starts in the cervix is referred to as cervical cancer, and it’s discussed in its own section of this website.
Types of Uterine Cancer
Types of Uterine Cancer
The most common type of uterine cancer starts in the lining of the uterus, or uterine wall, called the endometrium. This is why uterine cancer is also commonly referred to as endometrial cancer.
Types of uterine cancer include:
- Endometrial adenocarcinoma. The most common type of uterine cancer, starts in the glands of the endometrium. About 80 percent of uterine cancers are adenocarcinomas, and vary in degree of severity.
- Adenosquamous carcinoma. Comprising about ten percent of uterine cancers, adenosquamous carcinoma contains two types of cells: squamous cells (thin, flat cells that line certain organs) and gland-like cells.
- Papillary serous carcinoma. An aggressive cancer that tends to return even when caught early. It represents five percent of uterine cancers.
- Uterine sarcoma. A different type of cancer that develops in the uterine muscle wall (myometrium). It accounts for five percent of uterine cancer cases and spreads more quickly than endometrial cancer. There are many subtypes and they tend to spread through the bloodstream to the lungs.
Grading of your cancer
Grading is a way of dividing cancer cells into groups depending on how much the cells look like normal cells. This gives your doctor an idea of how quickly or slowly the cancer might grow and whether it is likely to spread.
The cells look very like normal cells. They are also called low grade or well differentiated. They tend to be slow growing and are less likely to spread than higher grade cancer cells.
The cells look more abnormal and are more likely to spread. This grade is also called moderately differentiated or moderate grade.
The cells look very abnormal and not like normal cells. They tend to grow quickly and are more likely to spread. They are called poorly differentiated or high grade.
Type 1 endometrial cancers (the most comon type) are low grade. And type 2 cancers are high grade.