Melanoma: Diagnosis

Approved by the Cancer.Net Editorial Board, 06/2017

ON THIS PAGE: You will find a list of common tests, procedures, and scans that doctors use to find out whether a suspicious mole or other skin growth is cancerous. Use the menu to see other pages.

Doctors use many tests to find, or diagnose, cancer. They also do tests to learn if cancer has spread to another part of the body from where it started. If this happens, it is called metastasis. For example, imaging tests can show if the cancer has spread. Imaging tests show pictures of the inside of the body. Doctors may also do tests to learn which treatments could work best.

For melanoma, a biopsy of the suspicious skin area, called a lesion, is the only sure way for the doctor to know whether it is cancer. In a biopsy, the doctor takes a small sample of tissue for testing in a laboratory. The doctor may suggest other tests that will help make a diagnosis and determine the overall stage of the melanoma.

This list describes options for diagnosing melanoma. Not all of the tests listed below will be used for every person. Your doctor will consider several factors, explained below, when choosing diagnostic tests for each person.

Biopsy and pathological examination of a skin lesion

Other tests can suggest that cancer is present, but only a biopsy can make a definite diagnosis. Before a biopsy, a health care provider will usually numb the area with a local anesthetic. Anesthetic is medication that blocks the awareness of pain. Then he or she will remove a part or all of the suspicious skin growth, typically making sure to preserve the entire lesion so the thickness of the potential cancer and its margin (healthy tissue around the lesion) can be carefully examined.

A pathologist then analyzes the sample(s) removed during the biopsy to figure out if the lesion is a melanoma. A pathologist is a doctor who specializes in interpreting laboratory tests and evaluating cells, tissues, and organs to diagnose disease.

The pathologist will write a report, called a pathology report, that should include the following information:

  • If the cells are dividing, which is called the mitotic rate, the report will include the type/subtype of melanoma and the thickness of melanoma

  • Presence or absence of ulceration

  • Presence of immune cells called tumor-infiltrating lymphocytes

  • Margin status, which describes whether melanoma cells can be seen at the edges of the biopsy sample

Additional information is described in detail below.

Clinical types of melanoma of the skin

The 4 most common types of skin, or cutaneous, melanoma are:

  • 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 of melanoma tends to occur in older people. It most commonly begins on the face, ears, and arms, on skin that is often exposed to the sun.

  • Nodular melanoma. This type accounts for about 15% of melanomas. It often appears rapidly as a bump on the skin. It is usually black, but it may be pink or red.

  • Acral lentiginous melanoma. This type of melanoma develops on the palms of the hands, soles of the feet, or under the nail bed. It sometimes occurs on people with darker skin. Acral lentiginous melanoma is not related to sun exposure.

Subtypes of melanoma defined by gene mutations

Melanoma cells are usually classified by histologic types (above), which are based on how they appear under a microscope. Recent information has shown that melanoma can also be classified into molecular (genetic) subtypes. These molecular subtypes are based on the distinct genetic changes of the melanoma cells, called mutations. These genetic changes include:

  • BRAF mutations. The most common genetic change in melanoma is found in the BRAF gene, which is mutated in about 50% of cutaneous melanomas.

  • NRAS mutations. NRAS is mutated in the tumors of around 20% of patients with melanoma.

  • NF-1 mutations. NF-1 mutations are present in the tumors of around 10% to 15% of patients with melanoma.

  • KIT mutations. These mutations occur more commonly in melanomas that develop from mucus membranes, melanomas on the hands or feet, or melanomas that occur in chronically sun-damaged skin, such as lentigo maligna melanoma.

Some melanomas do not have mutations in the BRAF, NRAS, NF-1, or KIT genes. These tumors have other genetic changes that cause them to grow. Researchers are currently trying to target the other mutations found in these tumors in clinical trials.

The classification of melanoma into different subtypes based on genetic changes can have a major effect on treatment options for advanced melanoma. Targeting specific mutated genes is an important new way of treating invasive melanoma, called targeted therapy. Learn more about targeted therapy in the Treatment Options and Latest Research sections.

Melanoma tumor thickness

The thickness of the primary melanoma tumor is the most reliable characteristic that helps doctors predict the risk that the cancer will spread. To do this, the pathologist will measure the depth of the melanoma from near the top of the skin down to the bottom of the melanoma in the underlying skin.

  • Thin. A melanoma tumor that is less than 1 mm thick is characterized as "thin." A thin melanoma is associated with a low risk of spreading to regional lymph nodes or to distant parts of the body.

  • Intermediate. An intermediate-thickness melanoma is between 1 mm and 4 mm.

  • Thick. A thick melanoma, more than 4 mm thick, is associated with a higher chance of recurrence. This is because the cancer has sometimes already spread to other parts of the body at the time of diagnosis. Recurrence is when a cancer comes back after treatment.


The presence or absence of ulceration of the primary melanoma is defined in the pathology report. Ulceration is the loss of the surface of the skin. If the melanoma is ulcerated, research has shown it significantly increases the risk of spread and recurrence.

Mitotic rate

Another pathological feature of melanoma is the mitotic rate, which is an estimate of the amount of cell growth. It is measured as the number of mitoses per millimeter squared (mm2). Combined with the thickness and the presence of ulceration, the mitotic rate may be used to help determine stage, treatment options, and prognosis (see below).

Additional evaluation after a diagnosis of melanoma

After an 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. 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 on the primary (original) melanoma’s risk of recurrence. For most low-risk melanomas, such as most people whose melanoma is less than 1 mm thick, no further search for metastases or spread is generally necessary. For people with higher-risk melanoma, more extensive testing, such as radiology tests described below, may be considered. Therefore, the extent of the initial evaluation for a person with newly diagnosed melanoma is based on the stage of melanoma and discussions with the team of doctors.

Depending on the results of the evaluation, including the pathology report of the primary melanoma tumor, further testing for high-risk or later-stage melanoma may include the following:

  • Ultrasound. An ultrasound uses sound waves to create a picture 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 3-dimensional picture of the inside of the body using x-rays taken from different angles. A computer combines these images into a detailed, cross-sectional view that shows any abnormalities or tumors. If melanoma has spread, a CT scan can be used to measure the tumor’s size. Sometimes, a special dye called a contrast medium is given before the scan to provide better detail on the image. This dye can be injected into a patient’s vein and/or given as a liquid to swallow.

  • Magnetic resonance imaging (MRI). An MRI uses magnetic fields, not x-rays, to produce detailed images of the body. MRI can be used to measure the tumor’s size. A special dye called a contrast medium is given before the scan to create a clearer picture. This dye is injected into a patient’s vein.

  • Positron emission tomography (PET) or PET-CT scan. A PET scan is usually combined with a CT scan (see above), called a PET-CT scan. However, you may hear your doctor refer to this procedure just as a PET scan. A PET scan is a way to create pictures of organs and tissues inside the body. A small amount of a radioactive sugar substance is injected into the patient’s body. This sugar substance is taken up by cells 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.

After 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.

The next section in this guide is Stages. It explains the system doctors use to describe the extent of the disease. You may use the menu to choose a different section to read in this guide.