Diagnosis of melanoma skin cancer
Diagnosis is the process of finding out the cause of a health problem. Diagnosing melanoma skin cancer usually begins with a visit to your family doctor. Your doctor will ask you about any signs or symptoms you have and do a skin exam. Based on this information, your doctor may refer you to a specialist, such as a dermatologist or surgeon.
The process of diagnosis may seem long and frustrating. It’s normal to worry, but try to remember that other health conditions can cause similar signs and symptoms as melanoma skin cancer. It’s important for the healthcare team to rule out other reasons for a health problem before making a diagnosis of melanoma skin cancer.
The following tests are usually used to rule out or diagnose melanoma skin cancer. Many of the same tests used to diagnose cancer are used to find out the stage (how far the cancer has spread).
Health history and physical exam
Your health history is a record of your signs and symptoms, risk factors and all the medical events and problems you have had in the past. Your doctor will ask questions about your history of:
- signs or symptoms that suggest melanoma skin cancer
- sun exposure and indoor tanning
- blistering sunburns
- atypical moles (dysplastic nevi) – they look different from normal moles
- skin cancer, both melanoma and non-melanoma
Your doctor may also ask about a family history of:
- skin cancer, both melanoma and non-melanoma
- risk factors for melanoma skin cancer, including familial atypical multiple mole melanoma (FAMMM) syndrome
A physical exam allows your doctor to look for any signs of melanoma skin cancer. A skin exam is often the first part of a physical exam. During a skin exam, your doctor will check the entire surface of your skin and look for any abnormal moles or areas. The doctor will check the size, shape, colour and feel of any moles.
During a physical exam, your doctor may also check for enlarged lymph nodes by feeling your neck, your groin or under your arms.
Dermoscopy is used to see areas of the skin more clearly. It also lets the doctor look at structures, such as blood vessels, that can’t be seen just by looking at the skin. It uses a tool (a dermoscope) with a special light and magnifying lens (microscope) that your doctor holds against the skin and looks through. Dermoscopy is also called dermatoscopy, epiluminescence microscopy, skin surface microscopy and incident light microscopy.
A device called the Verisante Aura may also be used to scan a mole or growth to find out if it is cancerous. Health Canada has approved the Aura, but it is not available at all centres and is not a standard way to diagnose melanoma and other skin cancers.
During a skin biopsy, the doctor removes tissues or cells from the skin so they can be tested in a lab. A report from the pathologist will confirm whether or not cancer cells are found in the sample. The type of biopsy used often depends on what the growth looks like and its size.
Excisional biopsy is a type of surgical biopsy that removes the entire growth using a scalpel (knife). It is done when the doctor thinks it could be melanoma skin cancer. An excisional biopsy is the best type of biopsy to make a proper diagnosis of melanoma skin cancer.
Punch biopsy removes a round part of the growth using a sharp tool called a punch. It may be done when the growth is very large and the doctor thinks it could be melanoma skin cancer. With the punch biopsy, the doctor tries to remove most of the abnormal area of the growth including part of the edge. Sometimes a punch is big enough to remove the entire growth. An incisional biopsy, which removes part of the growth using a scalpel, may be used instead of a punch biopsy.
Shave biopsy shaves off a growth on the skin using a flexible razor blade or a scalpel. It is sometimes used as long as the doctor can remove enough tissue.
Lymph node biopsy
A lymph node biopsy removes a lymph node or some lymph node tissue so it can be tested for cancer in a lab. It is done if the doctor thinks the cancer has spread to lymph nodes. A lymph node biopsy is also often part of the treatment for melanoma skin cancer.
Fine needle aspiration (FNA) uses a very thin needle to remove a small amount of fluid or cells from a lymph node. It may be done if the doctor feels an enlarged lymph node or an enlarged lymph node is found during an imaging test such as an ultrasound.
Sentinel lymph node biopsy (SLNB) is used to identify and remove the sentinel lymph node to see if it contains cancer cells. The sentinel node is the first lymph node in a group of lymph nodes that receives lymph fluid from around a tumour. An SLNB may be done if the melanoma on the skin is thicker than 1 mm. Doctors may also consider doing an SLNB for slightly thinner tumours (0.75 mm to 1 mm thick).
Cell and tissue studies
Cells and tissues can be studied in a lab to look for signs of cancer. They can show certain changes in the body. Melanoma skin cancer cell and tissue samples are usually collected during a biopsy. Tissue can also be removed during surgery.
The following cell and tissue studies may be done for melanoma skin cancer.
Mitotic rate measures how fast cancer cells are dividing and growing. It is the number of cells that divide (mitosismitosisThe process by which a cell divides to form 2 new cells. Each new cell receives a complete set of chromosomes from the original cell.) in a certain amount of cancer tissue. Mitotic rate is used to help stage melanoma skin cancer and decide on the best treatment.
BRAF is a gene that is changed (mutated) in about half of all melanoma skin cancers. A BRAF gene mutation can cause cancer cells to grow and divide quickly. Testing for the BRAF gene mutation is usually done on tumours in people with stage 4 melanoma skin cancer. Melanoma skin cancers that test positive for the BRAF gene mutation may respond to certain targeted therapy drugs.
Find out more about cell and tissue studies.
A computed tomography (CT) scan uses special x-ray equipment to make 3-D and cross-sectional images of organs, tissues, bones and blood vessels inside the body. A computer turns the images into detailed pictures.
A CT scan of the chest, abdomen and pelvis is used to check if melanoma skin cancer has spread to other parts of the body. It is usually done when melanoma skin cancer is thicker than 4 mm. It is also done if cancer is found in any of the lymph nodes.
Find out more about a CT scan.
Magnetic resonance imaging (MRI) uses powerful magnetic forces and radiofrequency waves to make cross-sectional images of organs, tissues, bones and blood vessels. A computer turns the images into 3-D pictures.
An MRI may be used to check if the doctor thinks that melanoma skin cancer has spread to the brain or spinal cord.
Find out more about an MRI.
An x-ray uses small doses of radiation to make an image of parts of the body on film. A chest x-ray may be used to check if the doctor thinks that melanoma skin cancer has spread to the lungs.
Find out more about an x-ray.
A positron emission tomography (PET) scan uses radioactive materials called radiopharmaceuticals to look for changes in the metabolic activity of body tissues. A computer analyzes the radioactive patterns and makes 3-D colour images of the area being scanned. A PET scan can be combined with a CT scan using the same machine (called a PET-CT scan).
A PET scan or PET-CT scan may be used to check if melanoma skin cancer has spread to lymph nodes or other parts of the body. It may be used before surgery to find out the amount of cancer there is and help decide if surgery should be done.
Find out more about a PET scan.
Blood tests measure certain cells or substances in the blood. They often provide helpful information about your general health, how some organs are working, other medical conditions and how you might respond to treatment.
Lactate dehydrogenase (LDH) is a tumour markertumour markerA substance in the body that may indicate the presence of a certain type of cancer. used to help stage advanced melanoma skin cancer and estimate a prognosis. Higher levels of LDH may mean that the melanoma skin cancer has spread to other parts of the body, such as the liver. It can also mean that the cancer will be harder to treat.
More blood tests such as a complete blood count and blood chemistry levels may be done before treatment is started.
Find out more about blood tests.