The uterus is part of a woman's reproductive system. It's a hollow organ in the pelvis.
The uterus has three parts:
- Top: The top (fundus) of your uterus is shaped like a dome. From the top of your uterus, the fallopian tubes extend to the ovaries.
- Middle: The middle part of your uterus is the body (corpus). This is where a baby grows.
- Bottom: The narrow, lower part of your uterus is the cervix. The cervix is a passageway to the vagina.
The wall of the uterus has two layers of tissue:
- Inner layer: The inner layer (lining) of the uterus is the endometrium. In women of childbearing age, the lining grows and thickens each month to prepare for pregnancy. If a woman does not become pregnant, the thick, bloody lining flows out of the body. This flow is a menstrual period.
- Outer layer: The outer layer of muscle tissue is the myometrium.
Cancer begins in cells, the building blocks that make up tissues. Tissues make up the uterus and the other organs of the body.
Normal cells grow and divide to form new cells as the body needs them. When normal cells grow old or get damaged, they die, and new cells take their place.
Sometimes, this process goes wrong. New cells form when the body doesn't need them, and old or damaged cells don't die as they should. The buildup of extra cells often forms a mass of tissue called a growth or tumor.
Tumors in the uterus can be benign (not cancer) or malignant (cancer). Benign tumors are not as harmful as malignant tumors:
- Benign tumors (such as a fibroid, a polyp, or endometriosis):
- are usually not a threat to life
- can be treated or removed and usually don't grow back
- don't invade the tissues around them
- don't spread to other parts of the body
- Malignant growths:
- may be a threat to life
- usually can be removed but can grow back
- can invade and damage nearby tissues and organs (such as the vagina)
- can spread to other parts of the body
Cancer cells can spread by breaking away from the uterine tumor. They can travel through lymph vessels to nearby lymph nodes. Also, cancer cells can spread through the blood vessels to the lung, liver, bone, or brain. After spreading, cancer cells may attach to other tissues and grow to form new tumors that may damage those tissues. See the Staging section for information about uterine cancer that has spread.