TNM system for melanoma
Melanoma stages are assigned based on the size or thickness of the tumor, whether or not it has spread to the lymph nodes or other organs, and certain other characteristics, such as growth rate.
The American Joint Commission on Cancer has developed a uniform staging system that allows doctors to determine how advanced a melanoma is, and to share that information with each other in a meaningful way. This melanoma staging system, known as TNM staging, is composed of three key pieces of information:
- Tumor (T) describes the tumor’s thickness, or how deep it has grown into the skin. The thickness of the melanoma, also known as the Breslow measurement, is an important factor in predicting whether or not a tumor has spread. The thicker the melanoma, the greater the chance of it spreading. The rate at which the tumor cells are dividing (also known as the mitotic rate), and the presence or absence of ulceration (an open, bleeding sore), are also considered in determining the T category.
- Nodes (N) indicates whether or not the melanoma cancer has spread to nearby lymph nodes, or the channels connecting the lymph nodes.
- Metastasis (M) refers to whether the melanoma has spread to distant organs, as well as on levels of LDH, a substance in the blood.
Melanoma may be staged before surgery (clinical staging), based on physical exam and imaging results. It will also be staged after surgery (pathologic staging), in which the clinical information will be combined with information gained from biopsies. Because it uses more information, pathologic cancer staging is the most accurate.