Staging Of Melanoma

Skin cancer most often appears in three common types: basal cell carcinoma, squamous cell carcinoma and melanoma. These are sometimes categorized as melanoma skin cancers and non-melanoma skin cancers. Staging is the process of identifying a skin cancer lesion by describing its size and the extent to which it has invaded the body’s tissues. Melanoma and non-melanoma skin cancer lesions can both be described using a standardized staging process.

The American Joint Commission on Cancer (AJCC) TNM System

Melanoma grading is determined by the AJCC TNM system:

  • T for tumor: The tumor is given a number (0-4) based on how far the lesion extends down into the skin. Tumor thickness is measured using a micrometer, a device used to make microscopic measurements. The thicknesses are sometimes described using Breslow staging. Melanoma T stage also includes mitotic rate, or the rate at which cell division is occurring in the tumor. Additionally, the tumor is also given a letter: “b” if it is ulcerated (meaning there is no layer of skin covering the lesion) or “a” if it is not ulcerated.
  • N for nearby lymph nodes: Lymph nodes are part of the body’s immune system. A number from 0-3 is assigned based on whether cancer cells are found to have spread to the lymph nodes or lymph channels.
  • M for metastasis: Metastasis is the spreading of cancer cells to distant parts of the body, forming secondary tumors.

How is the Melanoma Stage Determined?

Melanoma stages (0-4) are assigned based on the values of each component of the TNM system:

  • Stage 0: The tumor is confined to the epidermis.
  • Stage I: The tumor is confined to the skin. It may or may not be ulcerated, and measures from less than 1.0 to 2.0mm thick.
  • Stage II: The tumor is confined to the skin. It may or may not be ulcerated, and measures from 1.01 to 4.0mm thick.
  • Stage III: The tumor may or may not be ulcerated, and has spread to the lymph nodes.
  • Stage IV: The tumor has spread beyond the originally affected area of skin and lymph nodes to affect organs such as the brain or lungs.

Stages I-IV can be broken down into further sub-stages to classify the tumor’s features more specifically.

Other Types of Melanoma Staging

Clark’s level is also sometimes used for staging. This system assigns a number (1-5) to describe the depth of the tumor’s penetration into the different levels of skin. However, the AJCC’s TNM system is the current preferred method of staging for melanoma rather than the Clark melanoma levels.

Clinical vs. Pathologic Staging

Melanoma can be staged in two different ways. Clinical staging assigns a stage based on the clinical exam, skin biopsy and results of imaging tests. Clinical staging therefore refers to the primary tumor only.

Pathologic staging also takes into account results of biopsies of lymph nodes and other organs, and therefore accounts for all portions of the TNM staging system.

Resources

American Cancer Society. (2010). Melanoma skin cancer. Retrieved June 30, 2010, from http://www.cancer.org/acs/groups/cid/documents/webcontent/003120-pdf.pdf

National Cancer Institute. (2003). What you need to know about melanoma. Retrieved June 30, 2010, from http://www.cancer.gov/cancertopics/wyntk/melanoma/page12

National Cancer Institute. (2010). Melanoma treatment (PDQ). Retrieved June 30, 2010, from http://www.cancer.gov/cancertopics/pdq/treatment/melanoma/Patient/page2