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Doctors use many tests to diagnose cancer and find out if it has metastasized (spread). For melanoma, a biopsy of the suspicious skin area, called a lesion, is the only way to make a definitive diagnosis. The doctor may suggest other tests that will help make a diagnosis and determine the overall stage of the melanoma. Imaging tests may be used to find out whether the cancer has metastasized.
A biopsy and pathologic examination of a skin lesion for melanoma
A biopsy is the removal of a small amount of tissue (usually performed with a local anesthetic to numb the area) for examination under a microscope. The suspected skin lesion is removed using techniques that preserve the entire lesion so that the thickness of the potential cancer and its margin (healthy tissue around the lesion that is removed) can be carefully examined. The tissue sample is analyzed by a pathologist (a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease), who determines if it is a melanoma.
After a biopsy, the pathologist will write a report (called a pathology report) that should include the following information. Each of these items is described in detail below:
- Type/subtype of melanoma
- Thickness of melanoma
- Presence or absence of ulceration
- Mitotic rate
- Margin status
There are four types of skin melanoma:
- Superficial Spreading Melanoma: This is the most common type, accounting for 70% of melanomas. It usually develops from an existing mole.
- Lentigo Maligna Melanoma: This type tends to occur in older people. It most commonly begins on the face, ears, and arms on skin that is chronically exposed to the sun.
- Nodular Melanoma: This type accounts for about 15% of melanoma, often appears rapidly as a bump on skin. It is often black, but it may also be pink or red.
- Acral Lentiginous Melanoma: This type develops on palms, soles, or under the nail bed. It sometimes occurs on people with darker skin. Acral lentiginous melanoma is not related to sun exposure.
Recent information has shown that melanoma can also be classified into molecular subtypes based upon distinct genetic alterations in the melanoma rather than histologic types. The most common mutation or broken gene in melanoma is the BRAF (V600E) gene which is mutated in about 50% of melanomas. Another common mutation is the C-kit mutation. This occurs more commonly in melanomas that arise from the mucosal lining, acral lentiginous melanoma, or melanoma that arises from chronically sun damaged skin (such as lentigo maligna melanoma). The classification of melanoma into different subtypes based upon genetic alterations can have a major effect on treatment options, as targeting specific mutated genes is an important new way of treating advanced melanoma. Learn more about this approach, called targeted therapy, in the Treatment and Current Research sections.
The pathologist will measure the “thickness” of the melanoma in millimeters (or fraction of a millimeter) from the top of the skin down to the underlying skin because it is the most reliable feature reflecting the risk of spread. Other features include the mitotic rate (an estimate of the speed at which tumor cells are dividing), measured as the number of mitoses per millimeter squared (mm2). In addition, the presence or absence of ulceration of the primary melanoma is defined in the pathology report. If there is ulceration, research has shown it significantly increases the risk of the melanoma coming back after treatment (called recurrence or relapse), and it may predict whether adjuvant treatment with an immunotherapy called interferon will be beneficial after surgery (see Treatment).
The thickness, ulceration, and mitotic rate of the melanoma also determine the stage, treatment approach, and prognosis (see below). A thin melanoma, which means the tumor is less than 1 mm thick, is associated with low risk of spread to regional lymph nodes or to distant sites. An intermediate-thickness melanoma is between 1 mm and 4 mm. A thicker melanoma, greater than 4 mm thick, is associated with a greater chance of recurrence.
Additional patient evaluation after a diagnosis of melanoma
After the initial diagnosis of melanoma, you will be referred to a specialist. The doctor will take a complete medical history, noting any symptoms or signs, and perform a complete physical examination, including a total skin examination and an examination of regional (draining) lymph nodes. The focus of these examinations is to identify risk factors and signs or symptoms that may indicate melanoma has spread beyond the original site.
The extent of the initial evaluation is based upon the risk of recurrence associated with the primary (original) melanoma. In general, for most low-risk melanomas (such as those less than 1 mm), no further search for metastases or spread is necessary. In patients with higher-risk melanoma, more extensive testing (as described below) may be considered. Therefore, the extent of the initial evaluation for a patient with newly diagnosed melanoma depends upon on the stage and discussion with the team of doctors.
Depending on the results of the evaluation, including the pathology report of the primary melanoma tumor, testing may include the following blood tests and/or imaging studies.
Blood tests. The patient's blood may be tested to help determine if the cancer has spread. For melanoma, this may include a complete blood count and chemistry panel, which is a test that evaluates blood electrolytes (minerals in your body, such as potassium and calcium) and enzymes (specialized proteins) that can be abnormal if cancer has spread. In addition, the doctor may test to check the blood's level of lactate dehydrogenase (LDH; an enzyme that can help signal tissue damage) level. LDH is a tumor marker, which is a substance found in a patient's blood that is produced either by the tumor itself or by the body in response to the cancer.
X-ray. An x-ray is a way to create a picture of the structures inside your body, using a small amount of radiation.
Ultrasound. An ultrasound uses sound waves to create pictures of the internal organs, including collections of lymph nodes (called lymph node basins) and soft tissue.
Computed tomography (CT or CAT) scan. A CT scan creates a three-dimensional picture of the inside of the body with an x-ray machine. A computer then combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. Sometimes, a contrast medium (a special dye) is injected into a patient's vein to provide better detail.
Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. A contrast medium may be injected into a patient's vein to create a clearer picture.
Positron emission tomography (PET) scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive substance is injected into a patient's body. This substance is absorbed mainly by organs and tissues that use the most energy. Because cancer tends to use energy actively, it absorbs more of the radioactive substance. A scanner then detects this substance to produce images of the inside of the body.
Learn more about what to expect when having common tests, procedures, and scans.
After these diagnostic tests are done, your doctor will review all of the results with you. If the diagnosis is cancer, these results also help the doctor describe the cancer; this is called staging. Learn more about the first steps to take after a diagnosis of cancer.