For decades, doctors have been using “staging” – a standardized method of determining how far a cancer has spread – to understand their patients’ likelihood of metastasis. Each stage (Stage I-IV) represents a group of patients whose tumors share similar physical characteristics. As with other cancers, the staging system for melanoma was developed by the American Joint Committee on Cancer (AJCC).
The American Academy of Dermatology summarizes the AJCC’s melanoma staging guidelines as follows:
To help determine your stage, your doctor will need to measure the thickness of your melanoma from the skin biopsy sample. This is called the Breslow measurement. In general, melanomas less than about 1/25 of an inch thick have a low chance of metastasizing, while thicker melanomas have a greater chance. However, there are cases where thin melanomas metastasize and thicker ones do not.
Another factor doctors will consider is mitotic rate—that is, the rate at which cells are dividing in a certain amount of melanoma tissue. A higher mitotic rate usually indicates that the cancer is more likely to grow and spread.
Also, sentinel lymph node biopsy (SLNB), in which nearby lymph nodes are checked for cancer cells, can be important in staging your melanoma. X-rays, blood work and CT scans are also used to confirm stage.
What Staging Says About Your Tumor
Staging is used by physicians to determine the prognosis (or outlook) on cancer, and is therefore an important part of selecting treatment and follow-up care. Patients whose tumors meet the criteria for Stage I, are thought to have a better prognosis than those in Stage II, III, or IV, for example. The survival rates for each stage are listed in the table to left.
Using tumor biology to determine metastatic risk
Today, physicians have access to a new gene test, called DecisionDx™-Melanoma, which was designed to accurately classify high and low risk—regardless of how the cancer may spread and irrespective of the tumor’s physical appearance. Unlike staging, the gene expression profile test predicts the likelihood of metastasis by analyzing the activity of a specific set of genes within the tumor (see Test Overview). DecisionDx-Melanoma can help provide a clearer picture of your cancer’s likelihood to metastasize, which can be extremely helpful to you and your doctor in deciding how to most effectively manage the disease.