Melanoma: Diagnosis

Approved by the Cancer.Net Editorial Board, 02/2023

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

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

How melanoma is diagnosed

For melanoma, a biopsy of the suspicious skin area, called a lesion, is the only sure way for the doctor to know if 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.

There are different tests used for diagnosing melanoma. Not all of the tests described here will be used for every person. Your doctor will consider several factors 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 they 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 or dermatopathologist 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. A dermatopathologist is a pathologist or dermatologist with specialty training in diagnosing skin cancer and other disorders of the skin using a microscope and other laboratory tests.

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

  • Thickness of the melanoma

  • Presence or absence of ulceration

  • Mitotic rate, which is the frequency with which the cells are dividing

  • The type and/or subtype of melanoma

  • Presence of immune cells called tumor-infiltrating lymphocytes

  • Margin status, which describes whether melanoma cells can be seen at the deep and/or peripheral (side) edges of the biopsy sample

  • Presence or absence of certain markers associated with prognosis and/or response to different therapies

  • Presence or absence of cancer cells in the lymph vessels or blood vessels, which is called lymphovascular invasion

Additional information is described in detail below.

Types of melanoma of the skin defined by pathologists

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

  • Superficial spreading melanoma. This is the most common type, making up 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, arms, and other 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 (listed above), which are based on how the cells 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 specific genetic changes in 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 people with melanoma.

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

  • KIT mutations. These mutations occur more commonly in melanomas that develop from mucus membranes (mucosal melanoma), melanomas on the hands or feet (acral melanoma), 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 trying to target 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 the types of treatment used for advanced melanoma. Targeting specific mutated genes is an important way of treating invasive melanoma, called targeted therapy. Learn more about targeted therapy in the Types of Treatment 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 or fatty tissue below.

  • 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 is more than 4 mm thick and associated with a higher chance of coming back after treatment, called a recurrence. If this occurs, it is because the cancer has already spread to other parts of the body at the time of diagnosis.

It is important to note that tumor thickness applies only to melanomas that invade into the dermis layer of the skin (see Medical Illustrations). In cases of melanoma in situ (also called MIS), tumor thickness is not measured. Melanoma in situ involves only the epidermal layer of the skin, and tumor thickness is not applicable in this case.


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 that lies over the melanoma tumor. 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 frequency of cell growth. It is measured as the number of dividing cells (mitoses) per millimeter squared (mm2). Combined with the thickness and the presence of ulceration, the mitotic rate may be used to help determine prognosis, which is the chance of recovery.

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 and lymph node 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 people with thin melanoma (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 the imaging tests described below, may be considered, but this usually occurs after surgical management has been completed. 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 creates a picture of the internal organs, including collections of lymph nodes, called lymph node basins, and soft tissue, using sound waves.

  • Computed tomography (CT or CAT) scan. A CT scan takes pictures of the inside of the body using x-rays taken from different angles. A computer combines these pictures into a detailed, 3-dimensional image 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 contrast medium can be injected into a patient’s vein or given as a pill or liquid to swallow.

  • Magnetic resonance imaging (MRI). An MRI produces detailed images of the inside of the body using magnetic fields, not x-rays. 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 creates pictures of organs and tissues inside the body. 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 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. However, the amount of radiation in the substance is too low to be harmful. A scanner then detects this substance to produce images of the inside of the body.

Lymphatic mapping and sentinel lymph node biopsy

Lymph nodes are small, bean-shaped organs that help fight infection. Melanoma can grow deep into the inner layers of skin and spread to the lymph nodes and other parts of the body.

Sentinel lymph node biopsy — also called SLNB, sentinel node biopsy, or SNB, or lymphatic mapping — is a surgical procedure that helps the doctor find out whether the cancer has spread to the lymph nodes. When cancer spreads from the place where it started to the lymph nodes, it travels through the lymphatic system. If lymphatic fluid drains from the site of the original melanoma to 1 (or more) lymph node, that node is called the sentinel lymph node. Because melanoma can start anywhere on the skin, the location of the sentinel lymph nodes will be different for each patient, depending on where the cancer started. To find the sentinel lymph node, a dye and a harmless radioactive substance is injected into the dermis of the skin as close as possible to where the melanoma started, which is generally around the biopsy site and/or remaining skin lesion. The substance is followed to the sentinel lymph node. Then, the doctor (typically a surgical oncologist) removes 1 or more of these lymph nodes to check for melanoma cells, leaving behind most of the other lymph nodes in that area. These are sent to a pathologist, who analyzes the lymph nodes and then provides a report.

If melanoma cells are not found in the sentinel lymph node(s), no further lymph node surgery is needed. If the test finds that the sentinel lymph node contains melanoma, this is called a "positive sentinel lymph node." This means the disease has spread there.

In the past, after a positive sentinel lymph node was found, the removal of more lymph nodes, called lymph node dissection, was typically recommended. However, recent data shows that this procedure does not affect how long patients live. In most instances, close monitoring with regular physical exams and lymph node ultrasounds is recommended in place of a lymph node dissection (see Types of Treatment).

Lymphatic mapping and sentinel lymph node biopsy are usually recommended for people with a melanoma that is more than 0.8 mm thick or has ulceration. However, a sentinel lymph node biopsy may also be recommended by a surgical oncologist for some other melanomas that are less than 0.8 mm thick depending on other risk factors.

There are few side effects from sentinel lymph node biopsy, but a patient may experience infection, seroma (fluid buildup) near the surgical area, numbness, and reopening of the surgical area. Buildup of lymph fluid, called lymphedema, may sometimes occur. Talk with your health care team about what to expect and how side effects will be managed.

This information is based on the ASCO guideline, "Sentinel Lymph Node Biopsy for Melanoma." Please note that this link takes you to a different ASCO website.

After diagnostic tests are done, your doctor will review 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. Use the menu to choose a different section to read in this guide.