There are three ways that cancer spreads in the body.
Cancer can spread through tissue, the lymph system, and the blood:
- Tissue. The cancer spreads from where it began by growing into nearby areas.
- Lymph system. The cancer spreads from where it began by getting into the lymph system. The cancer travels through the lymph vessels to other parts of the body.
- Blood. The cancer spreads from where it began by getting into the blood. The cancer travels through the blood vessels to other parts of the body.
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 Wilms tumor spreads to the lung, the cancer cells in the lung are actually Wilms tumor cells. The disease is metastatic Wilms tumor, not lung cancer.
In addition to the stages, Wilms tumors are described by their histology.
The histology (how the cells look under a microscope) of the tumor affects the prognosis and the treatment of Wilms tumor. The histology may be favorable or anaplastic (unfavorable). Tumors with a favorable histology have a better prognosis and respond better to chemotherapy than anaplastic tumors. Tumor cells that are anaplastic divide quickly and under a microscope do not look like the type of cells they came from. Anaplastic tumors are harder to treat with chemotherapy than other Wilms tumors at the same stage.
The following stages are used for both favorable histology and anaplastic Wilms tumors:
In stage I, the tumor was completely removed by surgery and all of the following are true:
- Cancer was found only in the kidney and did not spread to blood vessels in the renal sinus (the part of the kidney where it joins the ureter) or to the lymph nodes.
- The outer layer of the kidney did not break open.
- The tumor did not break open.
- A biopsy was not done before the tumor was removed.
- No cancer cells were found at the edges of the area where the tumor was removed.