27 NCCN Guidelines for Patients ® : Melanoma, 2018 2 Tests for melanoma Review Review Cancer tests are needed if your skin shows signs of cancer. Cancer tests are used to plan treatment. Your health history and body exam inform your doctor about your health. Testing tissue removed from your body is the only way to know if you have melanoma. Tests of lymph nodes can show if cancer has spread. Blood tests monitor melanoma that has spread far to other parts of the body. Tests that take pictures of the inside of your body may show if the cancer has spread.