The lymph nodes must be evaluated before treatment is selected. To find out whether melanoma cells have spread, the physician starts by feeling the nearby lymph nodes. If the melanoma is on the arm, the nearest nodes are in the armpit; if on the leg, they are in the groin. For a melanoma on the head, the closest lymph nodes are usually on the neck on the same side. For a tumor on the trunk, the nodes in either the armpit or the groin could be involved.

When an enlargement or lump in a lymph node can be recognized by touch, it is called palpable. A palpable lymph node will be surgically removed in a node biopsy.

This node is sent to the pathology laboratory to be tested for the presence of malignant cells. If any are found, the patient usually has the other nodes in that lymph node basin removed. Then, additional, or adjuvant, treatments that stimulate the immune system and/or chemotherapy will be recommended.

Non-Palpable Nodes

Sometimes the lymph nodes are not palpable. When that is the case, one of two approaches will usually be followed:

• Wait-and-See: Some physicians advise a "wait-and-see" policy. No further surgery is done at this time, but the patient is asked to return at regular intervals for checkups.
• Remove nodes. Other physicians believe in removing all the nodes in the region of the tumor on the chance that there are hidden cancer cells. You will hear this procedure described by the technical term of a "radical node dissection." There is no definite proof that non-palpable lymph node removal should be performed as a preventive measure. It is a good idea for a melanoma patient to ask the physician about these options and the reasons why one or the other is recommended.
• Selective removal of lymph nodes. In this approach, only the sentinel node and nodes in the region of the primary tumor are removed. This method is being used with increasing frequency for melanomas that are more than 1.00 mm in depth. The surgery is less extensive than the radical node dissection, and studies have found that patients do well.

Microscopic nodal involvement

Palpable nodes may — or may not — be a sign of melanoma. The diagnosis must be confirmed by microscopic evaluation. This is also the procedure for sentinel nodes that are non-palpable, but may still contain cancerous cells. Research is now going on into special biochemical techniques that can identify those melanoma cells that do not show up under routine microscopic examination.

Local vs. Distant Spread

In local forms of the disease, the metastases can reach skin or subcutaneous tissue more than 2 cm from the primary tumor, but not beyond the regional lymph nodes. Once the disease has advanced to Stage IV, melanoma cells have traveled through the body via the bloodstream or lymph vessels, going far from the original tumor site. They may have reached distant lymph nodes or invaded the internal organs. This can be in addition to or instead of the local spread to the lymph nodes or in-transit metastases.

When distant metastases are suspected, they can be traced by scans of the
chest, head, abdomen and pelvis with a CT scan (computed tomography) in which special x-ray equipment and a computer program show a cross-section of body tissues or organs; an MRI (magnetic resonance imaging) which uses a magnet instead of x-ray to create a map of the patient's body; and by PET (positron emission tomography), an evolving radiographic technique. For PET scanning, radioactive sugar, the basic carbohydrate utilized by the body for energy, is injected intravenously into the patient. This sugar is taken up rapidly by any melanoma cells that are present.