Stage I. This category is subdivided according to the thickness of the primary (original) tumor.

• Stage 1a: The tumor is less than 1.0 mm in Breslow's thickness without ulceration and is in Clark's level II or III.
• Stage Ib: The tumor is less than 1.0 mm in Breslow's thickness with ulceration and/or Clark's level III or IV, or it is 1.01 - 2.0 mm in thickness without ulceration, and may have spread to the closest lymph nodes.

Stage II. This is also subdivided according to gradations in thickness and/or depth, the presence or absence of ulceration, and potential regional lymph node metastases.

• Stage IIa: The tumor is 1.01 - 2.0 mm in Breslow's thickness with ulceration, or is 2.01-4.0 mm in thickness without ulceration.
• Stage IIb: The tumor is 2.01-4.0 mm in Breslow's thickness with ulceration, or is greater than 4.0 mm in thickness without ulceration.
• Stage IIc: The tumor is greater than 4.0 mm in Breslow's thickness with ulceration.

If a melanoma is suspected to have spread to the lymph nodes at any point in Stage I or II, a test called a sentinel node biopsy is done to confirm this. This technique involves removing and examining the node nearest the tumor, which is called the sentinel node. Such a biopsy is now frequently done when a tumor is more than 1 mm in thickness, or when a thinner melanoma shows evidence of ulceration. If the sentinel node is found to be positive for melanoma, the rest of the surrounding lymph nodes are removed.

As the sentinel node biopsy is not considered necessary in all cases, you may wish to discuss the matter with your physician.

Later Stages — Stages III and IV

Stage III. Once a melanoma is known to have reached the local or regional lymph nodes, the disease is said to have reached Stage III. Breslow's thickness is no longer used in staging, but the presence of microscopic ulceration continues to be used, as it has an important effect on the progression of the disease.

In-transit or satellite metastases are also included in Stage III. In this case, the spread is to skin or underlying tissue (subcutaneous) for a distance of more than 2 centimeters (1 cm equals 0.4 inch) from the primary tumor, but not beyond the regional lymph nodes. In addition, the new staging system includes metastases so tiny they can be seen only through the microscope.

Stage IV. The melanoma has metastasized to lymph nodes far away from the primary tumor or to internal organs, most often the lungs, followed in descending order of frequency by the liver, brain, bone and gastrointestinal tract.