Squamous cell skin cancer is staged from 0 to 4, according to the American Cancer Society. These stages are determined by certain characteristics of the tumor, such as whether it has spread or not.
In Stage 0, the cancer is in situ, which means it's only found on the top layer of the skin, or epidermis, claims the American Cancer Society. It has not spread to any nearby lymph nodes or to distant organs in the body. This stage of cancer is easiest to treat.
In Stage 1, the cancer has not spread to nearby lymph nodes nor to distant organs, and the lesion is 2 centimeters across or smaller, says the American Cancer Society. It has no high-risk features. This means it has not grown thicker than 2 millimeters, and hasn't invaded the lower dermis, the nerves in the skin, the ears or the lip. The cells do not look extremely abnormal when viewed under a microscope.
Stage 2 is like Stage 1 except the tumor is at least 2 centimeters across and has at least two high-risk features, claims the American Cancer Society. In Stage 3, the tumor has invaded the bones of the face. It may have reached one nearby lymph node on the same side of the body.
In Stage 4, the tumor has invaded other bones and lymph nodes in the body and infiltrated the base of the skull, claims the American Cancer Society. Squamous cell carcinoma does not appear to spread to distant organs.