FAQ: How Is Skin Cancer Staged?

1 answer | Last updated: Sep 17, 2016
A fellow caregiver asked...

How is skin cancer staged?

Expert Answers

Dr. Leslie Kernisan is a senior medical editor at Caring.com and a clinical instructor in the University of California, San Francisco, Division of Geriatrics. She also provides housecalls and geriatric consultations in San Francisco.

Most skin cancers that require staging are melanomas. Although melanoma is the least common type of skin cancer, it's by far the most likely type to spread, and it's the cause of most skin cancer deaths.

Melanomas are staged using the TNM system, which stands for "tumor, node, and metastasis". These are assessed as follows:

  • T: Can be T1 through T4, depending on the thickness of the melanoma. A higher number (meaning a thicker melanoma) is more dangerous. An "a" or "b" after the number reflects whether the melanoma has an intact surface (a) or has started to turn into an open sore (b). Melanomas that become sores are considered higher risk.

  • N: Can be N0 through N3, depending on how many nearby lymph nodes have been invaded. A higher number is more dangerous.

  • M: Can be M0 if cancer hasn't spread beyond nearby lymph nodes. If there's been metastatic spread, it's coded M1a, M1b, or M1c, depending on which part of the body is affected. (M1c indicates more advanced disease.)

The TMN evaluation allows doctors to place patients in one of four stages of melanoma:

  • Stage I: Low-risk melonomas (T1a through T2a), with no sign of spread to lymph nodes or other parts of the body

  • Stage II: Thicker melanomas (T2b through T4b), with no sign of spread to lymph nodes or other parts of the body

  • Stage III: Melanomas with spread to the lymph nodes (N1 through N3) but no spread to other parts of the body

  • Stage IV: Melanoma that has spread beyond the nearby lymph nodes

A similar TNM staging can be used for squamous cell carcinoma of the skin, but this type of skin cancer only spreads to lymph nodes and beyond in 1 to 5 percent of cases.