Cancer may spread from where it began to other parts of the body.
When cancer spreads to another part of the body, it is called metastasis. Cancer cells break away from where they began (the primary tumor) and travel through the lymph system or blood.
- Lymph system. The cancer gets into the lymph system, travels through the lymph vessels, and forms a tumor (metastatic tumor) in another part of the body.
- Blood. The cancer gets into the blood, travels through the blood vessels, and forms a tumor (metastatic tumor) in another part of the body.
The metastatic tumor is the same type of cancer as the primary tumor. For example, if anal cancer spreads to the lung, the cancer cells in the lung are actually anal cancer cells. The disease is metastatic anal cancer, not lung cancer.
The following stages are used for anal cancer:
Stage 0 (Carcinoma in Situ)
In stage 0, abnormal cells are found in the innermost lining of the anus. These abnormal cells may become cancer and spread into nearby normal tissue. Stage 0 is also called carcinoma in situ.
Pea, peanut, walnut, and lime show tumor sizes.
In stage I, cancer has formed and the tumor is 2 centimeters or smaller.
In stage II, the tumor is larger than 2 centimeters.
In stage IIIA, the tumor may be any size and has spread to either:
- lymph nodes near the rectum; or
- nearby organs, such as the vagina, urethra, and bladder.
In stage IIIB, the tumor may be any size and has spread:
- to nearby organs and to lymph nodes near the rectum; or
- to lymph nodes on one side of the pelvis and/or groin, and may have spread to nearby organs; or
- to lymph nodes near the rectum and in the groin, and/or to lymph nodes on both sides of the pelvis and/or groin, and may have spread to nearby organs.
In stage IV, the tumor may be any size and cancer may have spread to lymph nodes or nearby organs and has spread to distant parts of the body.