After melanoma has been diagnosed, tests are done to find out if cancer cells have spread within the skin or to other parts of the body.
The process used to find out whether cancer has spread within the skin or to other parts of the body is called staging. The information gathered from the staging process determines the stage of the disease. It is important to know the stage in order to plan treatment.
The following tests and procedures may be used in the staging process:
- Physical exam and history: An exam of the body to check general signs of health, including checking for signs of disease, such as lumps or anything else that seems unusual. A history of the patient's health habits and past illnesses and treatments will also be taken.
- Lymph node mapping and sentinel lymph node biopsy: Procedures in which a radioactive substance and/or blue dye is injected near the tumor. The substance or dye flows through lymph ducts to the sentinel node or nodes (the first lymph node or nodes where cancer cells are likely to spread). The surgeon removes only the nodes with the radioactive substance or dye. A pathologist views a sample of tissue under a microscope to check for cancer cells. If no cancer cells are found, it may not be necessary to remove more nodes.
- CT scan (CAT scan): A procedure that makes a series of detailed pictures of areas inside the body taken from different angles. The pictures are made by a computer linked to an X-ray machine. A dye may be injected into a vein or swallowed to help the organs or tissues show up more clearly. This procedure is also called computed tomography, computerized tomography, or computerized axial tomography. For melanoma, pictures may be taken of the neck, chest, abdomen, and pelvis.
- PET scan (positron emission tomography scan): A procedure to find malignant tumor cells in the body. A small amount of radioactive glucose (sugar) is injected into a vein. The PET scanner rotates around the body and makes a picture of where glucose is being used in the body. Malignant tumor cells show up brighter in the picture because they are more active and take up more glucose than normal cells do.
- MRI (magnetic resonance imaging) with gadolinium: A procedure that uses a magnet, radio waves, and a computer to make a series of detailed pictures of areas inside the body, such as the brain. A substance called gadolinium is injected into a vein. The gadolinium collects around the cancer cells so they show up brighter in the picture. This procedure is also called nuclear magnetic resonance imaging (NMRI).
- Ultrasound exam: A procedure in which high-energy sound waves (ultrasound) are bounced off internal tissues, such as lymph nodes, or organs and make echoes. The echoes form a picture of body tissues called a sonogram. The picture can be printed to be looked at later.
- Blood chemistry studies: A procedure in which a blood sample is checked to measure the amounts of certain substances released into the blood by organs and tissues in the body. For melanoma, the blood is checked for an enzyme called lactate dehydrogenase (LDH). High LDH levels may predict a poor response to treatment in patients with metastatic disease.
The results of these tests are viewed together with the results of the tumor biopsy to find out the stage of the melanoma.
There are three ways that cancer spreads in the body. Cancer can spread through tissue, the lymph system, and the blood:
- Tissue: The cancer spreads from where it began by growing into nearby areas.
- Lymphatic system: The cancer spreads from where it began by getting into the lymphatic system. The cancer travels through the lymph vessels to other parts of the body.
- Blood: The cancer spreads from where it began by getting into the blood. The cancer travels through the blood vessels to other parts of the body.
Cancer may spread from where it began to other parts of the body:
When cancer spreads to another part of the body, it is called metastasis. Cancer cells break away from where they began (the primary tumor) and travel through the lymphatic system or blood.
- Lymphatic system: The cancer gets into the lymph system, travels through the lymph vessels, and forms a tumor (metastatic tumor) in another part of the body.
- Blood: The cancer gets into the blood, travels through the blood vessels, and forms a tumor (metastatic tumor) in another part of the body.
The metastatic tumor is the same type of cancer as the primary tumor. For example, if melanoma spreads to the lung, the cancer cells in the lung are actually melanoma cells. The disease is metastatic melanoma, not lung cancer.
Many cancer deaths are caused when cancer moves from the original tumor and spreads to other tissues and organs. This is called metastatic cancer. This animation shows how cancer cells travel from the place in the body where they first formed to other parts of the body.