The doctor also does a physical exam and, depending on the thickness of the tumor, may order chest X-rays, blood tests, and scans of the liver, lungs and brain. The most common tests ordered for melanoma patients include a chest X-ray (to look for spread to the lungs) and a blood test of the level of the enzyme lactic dehydrogenase (LDH). An elevated LDH level often occurs once cancer has spread to internal organs (liver or lungs).

Other blood tests may include:

• A complete blood count (CBC), which includes separate counts for red blood cells and white blood cells.
• Differential blood count, which includes a separate count for each type of white blood cell.
• Count of platelets, which are the cells in blood plasma that promote clotting.

In computed tomography (CT scan), several X-rays are taken from different angles. A computer then combines these images to make a cross-sectional image of a portion of the body. A (CT) scan of the abdomen is used if the doctor suspects that abdominal organs such as the liver are involved in the spread of cancer.

A CT of the pelvis is used if the doctor suspects that inguinal nodes - lymph nodes located in the groin area - may be cancerous or to identify whether the cancer has spread to lymph nodes in the pelvis. A CT scan of the head and neck may be performed to see if cervical nodes (lymph nodes in your neck) are involved. The doctor may also perform a CT scan of the chest region to see if cancer has metastasized to the lungs.

A bone scan may be necessary. A bone scan detects malignant bone tumors when X-ray findings are normal but cancer is suspected to have spread to the bone. A radioactive chemical is injected into a vein, and then the body is scanned with a special machine. Cancerous areas will be highlighted in the image produced by the scan.

To detect if the cancer has metastasized to the brain, the physician may perform an MRI (magnetic resonance imaging). This non-invasive procedure produces a similar but more specific image than a CT scan, using magnetic fields.

The most common method used to determine the stages of both melanoma and non-melanoma skin cancer is known as the TNM system. T stands for tumor (size and how far it has spread), N stands for whether cancer has spread to the lymph nodes and M is for metastasis (spread to distant organs).

After testing is completed, the cancer is given a stage from 0 to IV, according to how invasive the local tumor is and how far it has spread. The stage of the cancer helps determine treatment. The invasiveness of the local melanoma tumor is usually reported as the thickness of the tumor in millimeters (Breslow thickness). Another classification system, called the Clark system, describes the thickness of a melanoma in relation to layers of the skin.

Stage 0: Cancer is contained in the epidermis and has not spread to the dermis (in situ, non invasive). This corresponds with Clark Level I.

Stage I: The cancer appears to be confined to the skin and has not spread to the lymph nodes or distant parts of the body, such as the lungs or liver. The tumor is less than 1.5 millimeters (1/16 inch) thick and is Clark Level II (cancer cells are found in the papillary dermis, the layer of skin containing loose connective tissue, just below the epidermis) or Clark Level III (cancer fills the papillary dermis but does not penetrate the reticular dermis, the next layer of skin consisting of dense irregular connective tissue).

Stage IA: The tumor is 0.75 mm or less in thickness or Clark Level II. Stage IB: The tumor is between 0.75 mm and 1.5 mm in thickness or Clark Level III.

Stage II: The tumor is more than 1.5 millimeters thick or is Clark IV (cancer has invaded the reticular dermis but not the tissue beneath the skin) or Clark Level V (cancer has spread through the reticular dermis into the tissue beneath the skin). These tumors may be ulcerated (inflamed) or display signs of regression (decline in the size and severity of the melanoma). The cancer has not spread into the tissue below the skin, nearby lymph nodes (N0 or distant organs (M0).

Stage IIA: The tumor is more than 1.5 mm but less than 4 mm in thickness or Clark level IV. Stage IIB: The tumor is more than 4 mm thick or Clark level V.

Stage III: The melanoma has spread to nearby lymph nodes, or has spread to skin or underlying tissue (in-transit disease) near the site of the original melanoma. N1 metastases are 3 cm or less in dimension. N2 metastases are more than 3 cm in size. Stage III in-transit metastases affect the skin or tissue more than 2 cm from the original growth, but not the tissue beyond the nearby lymph nodes.

Stage IV: The cancer has spread beyond the original area of the growth and the nearby lymph nodes to other organs such as the lung, liver or brain, or to distant areas of the skin or lymph nodes M1.