Doctors rely on a variety of methods and tools to accomplish this. These generally include biopsy (removing skin, lymph-node samples, or other tissues and sending them to a pathology lab to be examined under a microscope); or, for more advanced cancers, imaging tests such as CT, MRI, or PET scans. (1) Accurate staging is vital for determining the best course of treatment. For people with advanced melanoma, for instance, researchers have, in recent years, developed breakthrough drugs that harness the power of the body’s own immune system to fight the disease. Doctors need to understand how far the cancer has progressed in order to identify the best candidates for these medications. Staging is also useful for considering survival rates — the percentage of people who live at least a certain amount of time after a cancer diagnosis. In general, the earlier the stage, the higher the survival rate. But it’s important to remember that individual cases vary considerably and that each person’s ability to recover from melanoma depends on a number of variables, including age and overall health. (2) As melanoma specialists learn more about how the disease develops and spreads, they are redefining each stage to match new insights into how important or irrelevant certain factors may be. Working together with cancer centers around the world, the American Joint Committee on Cancer (AJCC) updated the staging system that has been in effect since 2010. The new system officially launched in 2018. (3)
Understanding the Basics
Melanoma staging is extremely complex, with criteria that may be difficult to interpret for anyone who hasn’t been professionally trained in medicine. At its most basic level, the system employs a set of categories ranging from stage 0 (zero) to stage 4. The higher the number, the more advanced the cancer. Within each category, doctors also use the letters T, N, and M, assigning numbers to each to describe its severity:
T — the extent of the tumor. In general, the thicker the tumor, the harder the cancer is to cure. Ulceration (breakdown of the skin over the tumor that is visible under a microscope during a biopsy but not necessarily to the naked eye) is also a danger sign.
N — lymph nodes. Melanoma that has spread to nearby lymph nodes (clusters of small bean-shaped structures containing white blood cells) is more advanced.
M — metastasis. Cancer that has spread to distant lymph nodes or to organs like the lungs or brain is the most dangerous. (3)
Stage 0
A stage 0 tumor is in situ, meaning it is confined to the outermost layer of skin, the epidermis, and has not spread to nearby lymph nodes or distant sites.
Stage 1
The cancer is no more than 2 millimeters (mm) thick (this refers to how deeply it penetrates into the skin), may or may not be ulcerated, and hasn’t spread to nearby lymph nodes or distant sites.
Stage 2
The cancer is more than 1 mm thick and ulcerated, or more than 2 mm thick with or without ulceration, but there is no evidence of spread to nearby lymph nodes or distant sites.
Stage 3
Stage 3 melanomas have spread beyond the primary site, sometimes as far as the lymph nodes but no farther. There are several substages here, with two variations on stage 3B and four variations on stage 3C. The cancer is more severe the further down it is on the list.
Stage 3A
The tumor is no more than 2 mm thick and may or may not be ulcerated. It has spread to up to three lymph nodes, but is so small it can be seen only under a microscope.
Stage 3B
There is no sign of the primary cancer, and either the melanoma has spread to only one lymph node or it has spread to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor.
The cancer is no more than 4 mm thick and it may or may not be ulcerated. Additionally, either it has spread to only one lymph node; to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor; or to two or three lymph nodes.
Stage 3C
There is no sign of the primary cancer. Additionally, either it has spread to one or more lymph nodes; to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor; or to any lymph nodes that are clumped together.
The cancer is no more than 4 mm thick and it may or may not be ulcerated. Additionally, either it has spread to one or more lymph nodes; to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor; or to lymph nodes that are clumped together.
The cancer is between 2.1 and 4 mm thick; or it is thicker than 4 mm. It may or may not be ulcerated. Additionally, either it has spread to one or more lymph nodes; to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor; or to lymph nodes that are clumped together.
The cancer is thicker than 4 mm and is ulcerated. Additionally, either it has spread to no more than three lymph nodes; or to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor.
Stage3D
The cancer is thicker than 4 mm and is ulcerated. Additionally, either it has spread to four or more lymph nodes; or to very small areas of nearby skin (satellite tumors) or skin lymphatic channels around the tumor; or to lymph nodes that are clumped together.
Stage 4
The cancer can be any thickness and may or may not be ulcerated. It may or may not have spread to lymph nodes. However, it has spread to distant lymph nodes or organs such as the lungs, liver, or brain. (3)
