Melanoma is a type of skin cancer that develops from pigment-producing cells known as melanocytes. When melanoma is diagnosed early and treated promptly, it has a high cure rate. However, melanoma can be dangerous if it spreads from the skin to other parts of the body. So an important question after melanoma is diagnosed is: has it spread?
Doctors use several methods to determine if melanoma has metastasized (spread) from the original tumor site to other areas of the body. This helps them assign a stage to the melanoma, which guides treatment options and provides information about prognosis.
Physical exam
One of the first things a doctor will do is perform a complete physical exam. They will thoroughly inspect all lymph nodes near the original melanoma tumor, feeling for any enlarged nodes that could signal the cancer has spread there. Lymph nodes are small bean-shaped structures that filter bacteria and cells from lymph fluid throughout the body. Melanoma often spreads to nearby lymph nodes first before advancing to more distant sites.
In addition to checking lymph nodes, the doctor will closely examine the rest of your skin for spots that could be additional melanomas or melanoma metastases. About 10% of people with melanoma will develop additional melanomas later on.
Imaging tests
If there is any concern the melanoma has spread based on lymph node exam or symptoms, your doctor will order imaging tests. These provide pictures of the inside of the body and are used to search for melanoma metastases. Common imaging tests include:
– X-ray: An x-ray can detect melanoma that has spread to the lungs or bones.
– CT scan: This test takes cross-sectional images of the body. It is often used to look more closely at abnormal findings from an x-ray. CT scans can detect melanoma metastases in the lungs, liver, or other organs.
– PET scan: For a PET scan you are injected with a radioactive tracer. Areas of cancer show up brighter on the scan because cancer cells are more metabolically active. A PET scan can find melanoma that has spread throughout the body.
– MRI: An MRI uses radio waves and strong magnets to produce detailed images of the body’s organs and soft tissues. It can be used to detect melanoma metastases in soft tissue.
– Ultrasound: High-frequency sound waves are used to produce images of internal organs. Ultrasound can be used to look for melanoma spread in soft tissue and lymph nodes near the skin’s surface.
Lymph node biopsy
If imaging tests detect suspicious enlarged lymph nodes, your doctor may recommend a sentinel lymph node biopsy. This involves injecting a radioactive tracer and/or blue dye near the original melanoma tumor site. The lymph nodes that pick up the tracer first (the “sentinel” nodes) are the ones most likely to contain melanoma if it has spread. These lymph nodes can then be surgically removed and examined under a microscope for signs of melanoma.
A lymph node biopsy can provide a definitive answer regarding whether the cancer has traveled to the lymph nodes from the original skin tumor. If melanoma is found in the sentinel lymph nodes, your doctor will likely recommend removing more lymph nodes as well.
Blood tests
While they can’t directly detect metastases, certain blood tests may provide clues that the melanoma has spread. For example, elevated levels of an enzyme called lactate dehydrogenase (LDH) can indicate advanced melanoma. Doctors may also look for high levels of liver function enzymes, which can signify melanoma has reached the liver.
A blood test probably won’t be used as definitive proof of metastases on its own. But abnormal results may prompt your doctor to order imaging tests to look for melanoma elsewhere in the body.
Monitoring for high-risk melanoma
For early stage, thin melanomas, the tests described above are not usually ordered unless symptoms arise that suggest metastasis. But for higher risk melanomas, your doctor may wish to do baseline imaging like a CT scan before starting treatment. Then they will likely want to repeat the imaging at regular intervals to monitor for any new growths.
High risk features of primary melanomas that increase chances it has already spread or may eventually include:
– Breslow thickness >4 mm
– Ulcerated surface
– High mitotic rate (actively dividing cells)
– Certain subtypes like nodular melanoma
– Spread to lymph nodes observed on initial biopsy
For patients with these high risk primary tumors, close monitoring with imaging tests can help detect recurrences and metastases as early as possible when they are most treatable.
Factors affecting melanoma spread
Melanoma tumors can spread through either the:
– Lymphatic system – melanoma cells travel through lymph vessels to lymph nodes and other lymphatic tissue. Lymph node metastases often appear first.
– Bloodstream – melanoma gains access to blood vessels, allowing cells to spread hematogenously to distant sites like the liver, lungs and brain.
Some key factors that influence melanoma metastasis include:
Breslow thickness
The Breslow thickness is a measurement taken by the pathologist of the vertical depth of the primary melanoma tumor. In general, the thicker the tumor, the more likely it is to spread. Melanoma thickness is categorized as:
– Less than 1 mm – low risk of metastasis
– 1 to 2 mm – some risk
– 2 to 4 mm – moderate risk
– > 4 mm – high risk
Ulceration
An ulcerated melanoma has lost its top layer, breaking through the skin surface. Ulcerated melanomas are at higher risk of spreading than non-ulcerated tumors.
Mitotic rate
The mitotic rate indicates how rapidly melanoma cells are dividing and multiplying. Melanomas with a high mitotic rate have a greater metastatic potential.
Genetic mutations
Melanomas often contain mutations in genes like BRAF and NRAS that help drive their growth. Different mutations are linked to increased likelihood of metastasis. Testing for these mutations can provide prognostic information.
Location and subtype
Melanomas on certain areas of the body, like the scalp and neck, have higher odds of spreading. More aggressive subtypes like nodular melanoma also have greater metastatic potential.
Where does melanoma spread?
The most common sites where melanoma metastases appear include:
Lymph nodes
As explained above, lymph nodes near the primary tumor are often the first site of spread. Higher risk melanomas are more likely to reach the lymph nodes. From there, melanoma can continue traveling through the lymphatic system to more distant nodes and organs.
Lungs
The lungs are a common site of distant metastatic melanoma tumors. Melanoma spreads to the lungs hematogenously through the bloodstream. Lung metastases may be detected on an x-ray or CT scan.
Liver
The liver is another frequent site of distant melanoma metastasis. Tumors often spread to the liver from melanoma elsewhere in the body via the bloodstream.
Bones
The bones are the third most common site of distant melanoma metastasis. Spread to the bones also occurs through the blood. Bone metastases can be painful and weaken bones, increasing risk of fractures.
Brain
While less common than spreading to other organs, advanced melanoma can metastasize to the brain. Brain metastases cause neurological symptoms like headaches, seizures and vision changes.
Staging melanoma
If tests do indicate melanoma has spread, the cancer will be assigned a stage based on how far it has traveled:
Stage 0
Melanoma in situ, or melanoma present only in the outermost skin layer. It has not reached deeper layers or spread.
Stage 1
The primary melanoma tumor is less than 2 mm thick. No evidence of metastasis.
Stage 2
The primary melanoma tumor is 2 mm to 4 mm thick. Or, the tumor is thinner but has spread to a very small area of nearby skin. No distant metastasis.
Stage 3
Melanoma has spread to one or more nearby lymph nodes. Or, the primary tumor is thicker and has spread to lymph nodes or nearby skin. No distant metastasis.
Stage 4
Melanoma has metastasized to distant lymph nodes, organs, or skin sites far from the primary tumor.
Determining the stage of melanoma guides recommended treatment options. Earlier stages can usually be treated with surgery alone. Advanced stage 3 or 4 melanomas will require therapies like immunotherapy or targeted drugs.
Treatment when melanoma spreads
If melanoma has metastasized, treatment focuses on controlling the spread and managing symptoms. Options when melanoma has advanced beyond stage 2 may include:
– Immunotherapy drugs like ipilimumab or pembrolizumab work by boosting the immune system to attack melanoma tumors. They have led to long term remission for some metastatic melanoma patients.
– Targeted therapy drugs like vemurafenib and dabrafenib specifically inhibit the mutated BRAF protein found in many melanomas. This can destroy metastatic melanoma tumors with BRAF mutations.
– Radiation therapy can help shrink metastatic tumors and relieve pain in areas like the bones or brain.
– Surgery may be used to remove accessible metastases, such as those in the lung or liver.
– Chemotherapy may be given systemically or injected directly into tumors to destroy cancer cells.
– Clinical trials offer the chance to try promising new therapies.
– Palliative care helps control pain and symptoms to maintain quality of life.
The prognosis for metastatic melanoma varies greatly depending on how extensively it has spread, how rapidly it grows, and how well treatment works. With current therapies, the 5 year survival rate for stage 4 melanoma ranges from about 15-60%. Enrolling in clinical trials can provide access to newer treatments that may further improve prognosis.
Conclusion
Determining whether melanoma has spread beyond the skin is a critical factor guiding treatment. Doctors use exams, imaging tests, biopsies, and bloodwork to check for metastases in nearby lymph nodes or more distant sites like the lungs, liver, bones, and brain. If melanoma has advanced, newer treatments like immunotherapy and targeted drugs offer hope for controlling its spread and extending life. Catching melanoma metastases early on gives the best chance for treatment to be successful and for patients to achieve long-term remission.