How is melanoma skin cancer diagnosed?
Most melanomas are brought to a doctor’s attention because of signs or symptoms a person is having.
If an abnormal area of skin raises the suspicion of skin cancer, your doctor will do exams and tests to find out if it is melanoma, non-melanoma skin cancer, or some other skin condition. If melanoma is found, other tests may be done to determine if it has spread to other areas of the body.
Medical history and physical exam
Usually the first step your doctor takes is to get your medical history. The doctor will probably ask when the change on the skin first appeared, if it has changed in size or appearance, and if it is causing any symptoms (pain, itching, bleeding, etc.). You may also be asked about possible risk factors for skin cancer, such as your history of tanning and sunburns, and if you or anyone in your family has had skin cancer.
During the physical exam, your doctor will note the size, shape, color, and texture of the area(s) in question, and whether they are bleeding, oozing, or crusting. The rest of your body may be checked for moles and other spots that could be related to skin cancer.
The doctor may also feel the lymph nodes (small, bean-sized collections of immune cells) under the skin in the neck, underarm, or groin near the abnormal area. When melanoma spreads, it often goes to nearby lymph nodes first, making them larger. Enlarged lymph nodes might suggest that melanoma could have spread there.
If your primary doctor suspects melanoma, you may be referred to a dermatologist, a doctor who specializes in skin diseases, who will look at the area more closely.
Along with a standard physical exam, many dermatologists use a technique called dermatoscopy (also known as dermoscopy, epiluminescence microscopy [ELM], or surface microscopy) to see spots on the skin more clearly. The doctor uses a dermatoscope, which is a special magnifying lens and light source held near the skin. Sometimes a thin layer of alcohol or oil is used with this instrument. The doctor may take a digital photo of the spot.
When used by an experienced dermatologist, this test can improve the accuracy of finding skin cancers early. It can also often help reassure you that a spot on the skin is probably benign (non-cancerous) and doesn’t need a biopsy.
If the doctor thinks a spot might be a melanoma, a sample of skin will be removed from the suspicious area and sent to a lab to be looked at under a microscope. This is called a skin biopsy.
There are many ways to do a skin biopsy. The doctor will choose one based on the size of the affected area, where it is on your body, and other factors. Any biopsy is likely to leave at least a small scar. Different methods can result in different types of scars, so ask your doctor about scarring before the biopsy. No matter which type of biopsy is done, it should remove as much of the suspected area as possible so that an accurate diagnosis can be made.
Skin biopsies are done using a local anesthetic (numbing medicine), which is injected into the area with a very small needle. You will likely feel a small prick and a little stinging as the medicine is injected, but you should not feel any pain during the biopsy.
Shave (tangential) biopsy
For this type of biopsy, the doctor shaves off the top layers of the skin with a small surgical blade. Usually just the epidermis and the outer part of the dermis are removed, although deeper layers can be taken as well if needed. Bleeding from the biopsy site is stopped by applying an ointment, a chemical that stops bleeding, or a small electrical current to cauterize the wound.
A shave biopsy is useful in diagnosing many types of skin diseases and in sampling moles when the risk of melanoma is very low. This type of biopsy is not generally recommended if a melanoma is strongly suspected unless the biopsy blade will go deep enough to get below the suspicious area. Otherwise, if it is a melanoma, the biopsy sample may not be thick enough to measure how deeply the cancer has invaded the skin.
For a punch biopsy, the doctor uses a tool that looks like a tiny round cookie cutter to remove a deeper sample of skin. The doctor rotates the punch biopsy tool on the skin until it cuts through all the layers, including the dermis, epidermis, and the upper parts of the subcutis. The sample is removed and the edges of the biopsy site are often stitched together.
Incisional and excisional biopsies
To examine a tumor that might have grown into deeper layers of the skin, the doctor may use an incisional or excisional biopsy. For these types of biopsies, a surgical knife is used to cut through the full thickness of skin. A wedge or sliver of skin is removed for examination, and the edges of the cut are usually stitched together.
An incisional biopsy removes only a portion of the tumor. An excisional biopsy removes the entire tumor, and is usually the preferred method of biopsy for suspected melanomas if it can be done. But it is not always possible, so other types of biopsies may be needed.
Biopsies of melanoma that may have spread
Biopsies of areas other than the skin may be needed in some cases. For example, if melanoma has already been diagnosed on the skin, nearby lymph nodes may be biopsied to see if the cancer has spread to them.
Rarely, biopsies may be needed to figure out what type of cancer someone has. For example, some melanomas can spread so quickly that they reach the lymph nodes, lungs, brain, or other areas while the original skin melanoma is still very small. Sometimes these tumors are found with imaging tests (such as CT scans) or other exams even before the melanoma on the skin is discovered. In other cases they may be found long after a skin melanoma has been removed, so it’s not clear if it’s the same cancer.
In still other cases, melanoma may be found somewhere in the body without ever finding a spot on the skin. This may be because some skin lesions go away on their own (without any treatment) after some of their cells have spread to other parts of the body. Melanoma can also start in internal organs, but this is very rare, and if melanoma has spread widely throughout the body, it may not be possible to tell exactly where it started.
When melanoma has spread to other organs, it can sometimes be confused with a cancer starting in that organ. For example, melanoma that has spread to the lung might be confused with a primary lung cancer (cancer that starts in the lung).
Special lab tests can be done on the biopsy samples that can tell whether it is a melanoma or some other kind of cancer. This is important because different types of cancer are treated differently.
Biopsies of suspicious areas inside the body often are more involved than those used to sample the skin.
Fine needle aspiration biopsy
A fine needle aspiration (FNA) biopsy is not used on suspicious moles. But it may be used, for example, to biopsy large lymph nodes near a melanoma to find out if the melanoma has spread to them. For this type of biopsy, the doctor uses a syringe with a thin, hollow needle to remove very small pieces of a lymph node or tumor. The needle is smaller than the needle used for a blood test. A local anesthetic is sometimes used to numb the area first. This test rarely causes much discomfort and does not leave a scar.
If the lymph node is just under the skin, the doctor can often feel it well enough to guide the needle into it. For a suspicious lymph node deeper in the body or a tumor in an organ such as the lung or liver, an imaging test such as ultrasound or a CT scan is often used to help guide the needle into place.
FNA biopsies are not as invasive as some other types of biopsies, but they may not always collect enough of a sample to tell if a suspicious area is melanoma. In these cases, a more invasive type of biopsy may be needed.
Surgical (excisional) lymph node biopsy
This procedure can be used to remove an enlarged lymph node through a small incision (cut) in the skin. A local anesthetic (numbing medicine) is generally used if the lymph node is near the surface of the body, but the person may need to be sedated or even asleep (using general anesthesia) if the lymph node is deeper in the body.
This type of biopsy is often done if a lymph node’s size suggests the melanoma has spread but an FNA biopsy of the node was not done or did not find any melanoma cells.
Sentinel lymph node biopsy
If melanoma has been diagnosed and has any concerning features (such as being at least a certain thickness), a sentinel lymph node biopsy is often done to see if it has spread to nearby lymph nodes, which in turn might affect treatment options. This test can be used to find the lymph nodes that are likely to be the first place the melanoma would go if it has spread. These lymph nodes are called sentinel nodes (they stand sentinel, or watch, over the tumor, so to speak).
To find the sentinel lymph node (or nodes), a nuclear medicine doctor injects a small amount of a radioactive substance into the area of the melanoma. After the substance has travelled to the lymph node areas near the tumor, a special camera is used to see if the radioactive substance collects in one or more sentinel lymph nodes. Once the radioactive area has been marked, the patient is taken to where the surgery will be done and a blue dye is injected in the same place as the radioactive substance. A small incision is then made where the nuclear medicine doctor has marked, and the lymph nodes are then checked to find which one(s) became radioactive and turned blue. These sentinel nodes are removed and looked at under a microscope.
If there are no melanoma cells in the sentinel nodes, no more lymph node surgery is needed because it is very unlikely the melanoma would have spread beyond this point. If melanoma cells are found in the sentinel node, the remaining lymph nodes in this area are removed and looked at as well. This is known as a lymph node dissection (see “Surgery for melanoma skin cancer”).
If a lymph node near a melanoma is abnormally large, a sentinel node biopsy probably won’t be needed. The enlarged node is simply biopsied.
Lab tests of biopsy samples
Samples from any biopsies will be sent to a lab, where a doctor called a pathologist will look at them under a microscope for melanoma cells. Often, skin samples are sent to a dermatopathologist, a doctor who has special training in making diagnoses from skin samples.
If the doctor can’t tell for sure if melanoma cells are in the sample just by looking at it, special tests will be done on the cells to try to confirm the diagnosis. These tests have names such as immunohistochemistry (IHC), fluorescence in situ hybridization (FISH), and comparative genomic hybridization (CGH).
If the samples do contain melanoma, the pathologist will look at certain important features such as the tumor thickness and mitotic rate (the portion of cells that are actively dividing). These features help determine the stage of the melanoma (see the section “How is melanoma of the skin staged?”), which in turn affects treatment options and prognosis (outlook).
For people who have advanced melanoma, biopsy samples may be tested to see if the cells have mutations in certain genes, such as the BRAF gene. About half of melanomas have BRAF mutations. Some newer drugs used to treat advanced melanomas are only likely to work if the cells have BRAF mutations (see “Targeted therapy for melanoma skin cancer”), so this test is important in helping to determine treatment options.
Imaging tests use x-rays, magnetic fields, or radioactive substances to create pictures of the inside of the body. They are used mainly to look for the possible spread of melanoma to lymph nodes or other organs in the body. They are not needed for people with very early-stage melanoma, which is very unlikely to have spread.
Imaging tests can also be done to help determine how well treatment is working or to look for possible signs of cancer coming back (recurring) after treatment.
This test may be done to help determine whether melanoma has spread to the lungs.
Computed tomography (CT) scan
The CT scan uses x-rays to make detailed, cross-sectional images of your body. Unlike a regular x-ray, CT scans can show the detail in soft tissues (such as internal organs). This test can help tell if any lymph nodes are enlarged or if organs such as the lungs or liver have suspicious spots, which might be due to the spread of melanoma. It can also help show spread to the lungs better than a standard chest x-ray.
Instead of taking one picture, like a regular x-ray, a CT scanner takes many pictures as it rotates around you while you lie on a table. A computer then combines these pictures into detailed images of the part of your body that is being studied.
Before the scan, you may be asked to drink a contrast solution and/or get an intravenous (IV) injection of a contrast dye that helps better outline normal and abnormal areas in the body. You may need an IV line through which the contrast dye is injected. The injection can cause some flushing (a feeling of warmth, especially in the face). Some people are allergic and get hives or, rarely, more serious reactions like trouble breathing and low blood pressure. Be sure to tell the doctor if you have any allergies (especially to iodine or shellfish) or have ever had a reaction to any contrast material used for x-rays.
A CT scanner has been described as a large donut, with a narrow table that slides in and out of the middle opening. You need to lie still on the table while the scan is being done. CT scans take longer than regular x-rays, and you might feel a bit confined by the ring while the pictures are being taken.
CT-guided needle biopsy: CT scans can also be used to help guide a biopsy needle into a suspicious area within the body. For this procedure, you stay on the CT scanning table while the doctor moves a biopsy needle through the skin and toward the suspicious area. CT scans are repeated until the needle is in the mass. A needle biopsy sample is then removed and looked at under a microscope.
Magnetic resonance imaging (MRI) scan
Like CT scans, MRI scans give detailed images of soft tissues in the body. But MRI scans use radio waves and strong magnets instead of x-rays to create pictures. A contrast material might be injected, just as with CT scans, but is used less often.
MRI scans are very helpful in looking at the brain and spinal cord.
MRI scans take longer than CT scans – often up to an hour – and are a little more uncomfortable. You may have to lie inside a narrow tube, which is confining and can upset people with a fear of enclosed spaces. Newer, more open MRI machines can sometimes be used instead, but the images might not be as sharp in some cases. The MRI machine also makes loud buzzing noises, so some places provide earplugs to help block this noise out.
Positron emission tomography (PET) scan
A PET scan can help show if the cancer has spread to lymph nodes or other parts of the body. It is most useful in people with more advanced stages of melanoma – it is not usually done in people with early-stage melanoma.
For this test, you are injected with a radioactive substance (usually a type of sugar related to glucose, known as FDG). The amount of radioactivity used is very low and will pass out of the body over the next day or so. Because cancer cells in the body are growing quickly, they absorb more of the radioactive sugar. After about an hour, you are moved onto a table in the PET scanner. You lie on the table for about 30 minutes while a special camera creates a picture of areas of radioactivity in the body. The picture is not detailed like a CT or MRI scan, but it can provide helpful information about your whole body.
Many centers have special machines that can do both a PET and CT scan at the same time (PET/CT scan). This lets the doctor compare areas of higher radioactivity on the PET scan with the more detailed appearance of that area on the CT scan.
For more information on these imaging tests, see our document Imaging (Radiology) Tests.
Blood tests aren’t used to diagnose melanoma, but some tests may be done before or during treatment, especially for more advanced melanomas.
Doctors often test blood for levels of a substance called lactate dehydrogenase (LDH) before treatment. If the melanoma has spread to distant parts of the body, a high LDH level is a sign that the cancer may be harder to treat. This affects the stage of the cancer (see “How is melanoma skin cancer staged?”).
Other tests of blood cell counts and blood chemistry levels may be done in a person who has advanced melanoma to see how well the bone marrow (where new blood cells are made), liver, and kidneys are working during treatment.
Last Medical Review: 03/19/2015
Last Revised: 02/01/2016