The stages of a melanoma tumor are Stage 0, Stage I, Stage II, Stage III and Stage IV, says the National Cancer Institute. Stage 0 is also called melanoma in situ and means that abnormal cells are found on the top layers of the skin.
Stage I is divided into Stage IA and IB. In 1A, the tumor is less than a millimeter thick and has no ulceration, says NCI. In IB, the tumor is still less than 1 millimeter thick but has ulcerated. It can also be more than 1 but less than 2 millimeters thick with no ulceration.
Stage II is divided into IIA, IIB and IIC. In Stage IIA, the cancer is more than 1 but less than 2 millimeters thick and has ulcerated, explains NCI. A Stage IIA melanoma can also be more than 2 but less than 4 millimeters thick with no ulceration. In IIB, the cancer is more than 2 but less than 4 millimeters thick and has ulcerated, or it can have no ulcerations but be more than 4 millimeters thick. In Stage IIC, the cancer has grown to more than 4 millimeters thick and has ulcerated.
In Stage III, the cancer can be any thickness and can present with or without ulceration, reports NCI. However, it has spread to at least one lymph node or is found in a lymph vessel between the tumor and a local lymph node. The cancer is also found more than 2 centimeters from its primary tumor. The lymph nodes are matted together, or tiny tumors are found under the skin near the primary tumor. In Stage IV, the cancer has metastasized to distant sites.