How is Skin Cancer Staged and Classified?

This is the seventh page in the Understanding Skin Cancer Guide. This guide was developed by the HealthTree Education Team and was last updated and reviewed on May 14, 2026.

Doctors use "stages" to describe how far cancer has grown and whether it has spread. Knowing the stage of your cancer helps your care team plan the best treatment and understand your prognosis.

Skin cancer staging is most detailed and clinically important for melanoma. Basal cell carcinoma and squamous cell carcinoma are also formally staged using TNM criteria, though most cases are caught before they spread and staging has less impact on treatment decisions. This page focuses primarily on melanoma staging, with an overview of staging for other types.

The TNM Staging System

Most skin cancers are staged using the TNM system developed by the American Joint Committee on Cancer (AJCC). Each letter is assigned a number that describes how far the cancer has progressed in that category:

• T (Tumor) describes the thickness of the primary tumor (measured in millimeters) and whether it has certain high-risk features such as ulceration.
• N (Nodes) describes whether cancer has reached nearby lymph nodes, scored N0 (none) to N3 (extensive lymph node involvement).
• M (Metastasis) describes whether the cancer has spread to distant organs, scored M0 (no spread) or M1 (spread detected).

Melanoma stage groups

TNM staging for melanoma can be simplified into stages (0–IV). The larger the number, the more advanced the cancer.

Stage 0 — Melanoma In Situ

Abnormal melanocytes are found only in the outer layer of skin (the epidermis) and have not grown into deeper layers.

TNM example: Tis, N0, M0. The melanoma is entirely contained within the epidermis and has not invaded the dermis, lymph nodes (N0), or distant organs (M0).

Stage I

The melanoma is thin and localized to the skin. There is no spread to lymph nodes or distant organs.

TNM examples:

• Stage IA. T1a, N0, M0. The tumor is 1 mm or less thick and is not ulcerated. Low risk of spread.
• Stage IB. T1b or T2a, N0, M0. The tumor is 1 mm or less with ulceration, or 1 to 2 mm without ulceration. No lymph nodes or distant spread.

Stage II

The melanoma is thicker but is still confined to the skin with no spread to lymph nodes or distant organs. Stage II is divided into IIA, IIB, and IIC based on tumor thickness and ulceration.

TNM examples:

• Stage IIA. T2b or T3a, N0, M0. The tumor is 1 to 2 mm with ulceration, or 2 to 4 mm without ulceration. No nodal or distant spread.
• Stage IIB. T3b or T4a, N0, M0. The tumor is 2 to 4 mm with ulceration, or more than 4 mm without ulceration. No nodal or distant spread.
• Stage IIC. T4b, N0, M0. The tumor is more than 4 mm thick with ulceration. No nodal or distant spread. This is the highest-risk localized melanoma.

Stage III

The melanoma has spread to nearby lymph nodes or to nearby skin (satellite tumors or in-transit metastases), but not to distant organs. Stage III is divided into IIIA, IIIB, IIIC, and IIID based on the extent of regional spread.

TNM examples:

• Stage IIIA. T1 to T2a, N1a to N2a, M0. A thinner primary tumor with microscopic spread to 1–3 lymph nodes. No distant spread.
• Stage IIIB to IIID. Increasingly extensive regional lymph node involvement or in-transit/satellite metastases, but no distant spread.

Stage IV (metastatic melanoma)

The melanoma has spread to distant organs. Stage IV is divided based on the site of distant spread and LDH levels:

• M1a. Spread to distant skin, muscle, or lymph nodes. Normal LDH.
• M1b. Spread to the lungs.
• M1c. Spread to other non-brain distant organs.
• M1d. Spread to the brain.

Staging for basal cell and squamous cell carcinoma

Basal cell carcinoma and squamous cell carcinoma are also staged, though most cases are caught at an early stage. Your doctor will look for certain features that may indicate a higher risk and could affect your treatment plan, including:

• The size of the tumor, specifically whether it is larger than 2 centimeters
• Whether the cancer has grown into deeper tissue such as bone or nerves
• Where the tumor is located. Some areas of the body, such as the ear or lip, are considered higher risk
• How the cancer cells look under a microscope. Some cells appear more aggressive than others
• Whether the cancer has spread to nearby lymph nodes. This is uncommon, but more possible with squamous cell carcinoma

Recurrent skin cancer

Sometimes skin cancer can come back after treatment. This is called recurrent skin cancer. It may return in the same area where it was first found, in nearby lymph nodes, or in other parts of the body. If your cancer does come back, your care team will work with you to determine the best next steps based on where it has returned and what treatments you have already had.