Like most types of cancer, squamous cell carcinoma can be classified according to stage. The stages, which are given roman numerals from 0 to IV, describe how far the cancer has advanced. Squamous cell carcinoma stages are determined based on the TNM system of characteristics, which includes the tumor (its size, location, and depth), the nearby lymph nodes (whether the cancer has spread to these immune system structures) and metastasis (how far throughout the body the cancer has spread). Based on considerations for each of those characteristics, the cancer can be staged anywhere from 0 to IV. Stage 0 means there's no spread and the tumor is only on the top layer of skin, and stage IV means the cancer has spread to distant organs, lymph nodes, and other tissue.