Once the diagnosis of melanoma has been established, the key question is whether it has spread beyond the primary tumor. Melanoma can spread in three ways:

• Through the local tissues (the skin adjoining the tumor)
• Through lymph vessels near the tumor to the regional draining lymph nodes
• Through the blood vessels in the lower layers of the skin to the lungs

If the melanoma has spread beyond the local tissues, it has generally spread through the lymphatic system, a network of vessels and nodes that carry lymph throughout the body. Lymph, an almost colorless fluid, contains cells that help fight infection and disease. It bathes the cells of the body with water and nutrients, and carries away waste products and other impurities such as bacteria, viruses, and cancer cells. Each part of the body drains lymph through its own network of vessels and regional lymph nodes. The function of the lymph nodes is to filter lymph, trap impurities, and fight infection. Once lymph has been filtered, it is returned to the system.

To find out whether melanoma cells have escaped the primary tumor, the physician will examine the nearby lymph nodes to which the melanoma drains. If these lymph nodes feel abnormally hard or large, a biopsy is performed, in which a tissue sample is taken from the lymph node. This tissue is then examined by a pathologist, a doctor who specializes in identifying diseases by noting microsopic changes in organs, tissues, and fluids.

There are two types of lymph node biopsies:

• Needle biopsy (fine needle aspiration) is performed with local anesthetic. A slender needle is placed through the skin and into the suspicious lymph node. A small tissue sample is removed when the needle is withdrawn.
• Open biopsy is a surgical procedure to remove all or part of the lymph node. The nature of the surgery and type of anesthetic depend on the size and location of the lymph nodes.