Like most types of cancer, Merkel 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. Stages are determined by considering several characteristics, including the size of the tumor and how far the cancer has spread. The stages are:
- Stage 0: tumor is very small and confined to the upper layers of skin.
- Stage I: tumor is under 2 centimeters in diameter and hasn't spread.
- Stage II: tumor is larger than 2 centimeters and may have spread to nearby tissue like bone, muscle, connective tissue, or cartilage.
- Stage III: tumor is any size and has spread to nearby tissue and lymph nodes.
- Stage IV: tumor is any size and has spread to distant organs, such as the lung, liver, bone, or brain.