A cancer is often staged to describe the size and degree of spread to lymph nodes and other organs. It enables the doctor to decide on the treatment and probable prognosis or outcome of the cancer. Anal cancer is divided into the following stages
Stage 0

Abnormal cells are detected in the innermost lining of the anus.
Stage I

The tumor is
2 cm or less in size and has not spread to lymph nodes or other organs
Stage II

The tumor is
more than 2 cm in size and has not spread to lymph nodes or other organs
Stage III

The tumor may be of any size and
has invaded either nearby lymph nodes or organs
It is divided into stage III A and stage III B depending on the lymph nodes involved
Stage IV
The tumor has
spread to distant organs such as lungs and liver or bones