Spread of Melanoma

What Happens When I Have a Melanoma?

After a melanoma is diagnosed, the next step is to determine whether the melanoma has managed to metastasise (spread) or not (called staging the disease). Accurate staging is important to determine the most appropriate treatment. There are several methods for determining whether a melanoma has spread or not and these are discussed below. Firstly, however, the factors that influence the risk of spread are discussed.

Spread Risk of Melanoma

Does the Depth of Melanoma Increase the Risk of Spreading?

The risk that a melanoma has spread is most strongly related to the depth that the melanoma has managed to penetrate into the dermis of the skin. The depth of penetration is measured in millimetres and is called the Breslow depth. All melanomas start in the epidermis of the skin and while confined to this layer (then known as an in-situ melanoma) there is no risk of spread. Once a melanoma has penetrated from the epidermis into the dermis of the skin it then comes into contact with capillaries (small blood vessels) and lymphatic channels. The deeper a melanoma has penetrated into the skin, the more capillaries and lymphatic channels it has come into contact with. There is thus a higher risk of invasion into these structures with a resultant greater risk of spread (metastasis) to lymph glands and organs.

Other major features of a primary melanoma that determine the risk of spread are whether it has formed a sore (ulceration) and the number of actively dividing cells (mitotic cells) seen per high power field (60 times magnification) under the microscope.

Where do Melanomas Spread to?

If a melanoma metastasises the first site of spread in 90% of cases is to the regional lymph nodes. If the primary melanoma was on the leg, spread to lymph glands in the groin is most likely, while spread to glands in the arm pit (axilla) is most likely from a melanoma on the arm. The minority of melanomas (10%) will spread only via the blood stream and completely bypass the lymph glands. 

How Deep Must a Melanoma be to Spread?

Once a melanoma has penetrated from the epidermis into the dermis, the possibility of spread exists. Initially, with minimal invasion, the risk of spread is small (less than 1%). As the depth of invasion increases so does the risk that spread may have occurred. Risk of spread remains low (less than 5%) up to a Breslow depth of 0.8mm. Once a melanoma penetrates deeper than 0.8mm into the dermis, the risk of spread jumps straight to 15 to 20%. So a depth of penetration of 0.8mm is the threshold between a low risk of spread and a much higher risk. Ulceration (the melanoma has formed a sore) and a high mitotic count (one or more actively dividing cells seen per high power field under the microscope) also increase the risk of spread which means that melanomas thinner than 0.8 mm with these features can also have a 15 to 20% risk metastases.

What Does it Mean if Melanoma has Spread to the Lymph Glands?

The most significant determinant of prognosis in melanoma is the status of the lymph nodes. If there has been no spread (metastasis) to the lymph nodes then prognosis is good but even if there is microscopic spread to the lymph nodes it means that there is a higher risk of spread via the blood stream to internal organs. The greater the number of lymph glands that are involved by metastases and the greater the number and size of metastases within each lymph gland, the higher the risk of spread to internal organs.

Clinical Examination for Melanoma Spread

Will My Whole Body be Examined?

Prior to the actual examination it is important to find out about any unusual or persistent symptoms that a person with a melanoma may be experiencing. A good rule of thumb is that any new symptom (headache, dizziness, arm or leg weakness, persistent cough, abdominal pain, change in bowel habits, etc.) that has been present for two or more weeks and is unrelated to any concurrent illness (flu, gastro-enteritis, bronchitis, etc.) may be as a result of melanoma spread. A thorough clinical examination is a vital part of melanoma assessment. Firstly, one has a look at the skin to assess whether there are any additional melanomas on the skin surface. The skin around the primary melanoma biopsy site is felt to make sure that there are no signs of any tumour nodules sitting under the surface of the skin (these are known as satellite lesions). The lymph glands are then felt (palpated) in all areas to feel for any enlargement. Finally, the abdomen is examined to feel for enlargement of the liver and spleen and to exclude any abdominal masses.

Scans for Assessing Melanoma Spread

Why do I Need to Have a Scan for Melanoma?

Scans are done to assess whether the melanoma has spread (metastasised). The complexity (and expense) of the scans is determined by the risk of spread.

Types of Scans Used to Assess Melanoma Spread


If there is a low risk of spread (melanoma thinner than 0.8 mm with no ulceration or mitoses) then the only scan that is required is an X-ray of the lungs. The reason for this is that the lungs are the most common organ that melanomas spread to and it is cheap, easy and accurate to exclude spread with an X-ray of the chest.

CT Scan

If the melanoma has penetrated more deeply (melanoma thicker than 0.8 mm) and thus has a higher risk of spread to the lymph glands and internal organs, then a CT scan of the chest, abdomen and pelvis is advised as a screening method.

MRI Scan

If metastases to the brain are suspected (headaches, dizziness, paralysis, memory loss, confusion, etc.) then an MRI scan is the most accurate way of assessing this area. MRI is also used as a means to increase the accuracy of diagnosis of suspicious areas seen within the liver on ultrasound or CT scan.

Ultrasound Scan

If an enlarged lymph gland is detected on clinical examination, then an ultrasound scan of the lymph nodes is requested. An ultrasound scan gives the most accurate assessment of lymph node metastases.


Overall, the most accurate scan for assessing the spread of melanoma is a PET-CT scan (PET stands for positron emission tomography and this scan is combined with a standard CT scan). Unfortunately, this scan is considerably more expensive and hence medical aids will only cover the cost if spread has been proven to one or more sites. It is most commonly requested when spread to the sentinel lymph node has been detected (see below) to more accurately assess whether further spread has occurred to any of the internal organs. If a scan is clear in someone who has had a melanoma, it does not exclude microscopic spread. There is no scan that can detect microscopic deposits of melanoma in the lymph glands or organs. Unfortunately, microscopic deposits of melanoma can continue to grow and it is therefore necessary to continue regular follow-ups and scans. PET-CT scans are done at the Cape PET-CT Centre at Panorama Mediclinic Hospital, Cape Town. 

It is important to note that no type of scan can detect microscopic melanoma disease.

Biopsies for Melanoma

How do I know if My Enlarged Lymph Node Contains Melanoma or Not?

If an enlarged lymph node is detected on clinical examination and an ultrasound scan does not definitively show disease (pathology), then a fine needle aspiration (which sucks up some cells) of the enlarged gland is performed to obtain cells for analysis. If this still does not provide a definitive answer about the status of the gland, then it needs to be removed (biopsied) so that it can be analysed in the pathology laboratory. This would normally be done at the same time as the wide local excision of further skin around the site of the melanoma. If a firm lump is felt under the skin close to the primary melanoma site, this may be a satellite nodule and this may need a biopsy to establish the diagnosis.

Blood Tests for Melanoma

Will a Blood Test Show if I Have a Melanoma Metastasis or Not?

There are blood tests available which can be used to screen for melanoma metastases. A raised level of the liver enzyme, lactate dehydrogenase (LD) at diagnosis, is associated with a higher risk of metastases and a worse prognosis (even though no metastases may be seen in the liver). There is a protein marker on melanoma cells called S100B that can be measured in the blood. It is not used to diagnose melanoma metastases, however. If a patient has had a melanoma metastasis surgically resected and there are no other detectable metastases, one can measure the S100B levels to get a baseline. The S100B levels can then be re-measured every 3 to 6 months. If there is a rapid rise in the S100B levels, this is suggestive of a new metastasis. The problem with using S100B is that there are many falsely high readings. We, therefore, do not make regular use of this blood test.

Sentinel Lymph Node Biopsy for Melanoma

Why do I need a Sentinel Lymph Node Biopsy?

The most important advancement for the screening of melanoma metastases has been the development of the sentinel lymph node biopsy. This technique allows one to accurately identify the single lymph gland within a lymph node region (such as the groin, neck or axilla) that has the greatest likelihood of harbouring a metastasis (there are approximately 30 lymph glands in each region). This test is only done if no enlarged lymph nodes are evident on examination and was developed to be able to identify lymph glands with microscopic spread that would not be detected on routine scans. With practice, it is possible to accurately identify the sentinel lymph gland 99% of the time. If the sentinel gland contains no melanoma, then one can be 99% sure that none of the other glands within that region have melanoma metastases. This is very important information because people who have no spread to their lymph glands have a good prognosis, while those in whom there has been even a microscopic amount of spread, the prognosis is worse. Prior to the development of the sentinel lymph node biopsy technique, it was standard practice to remove all the lymph glands from the region draining the melanoma. This meant that about 80% of patients had a large and unnecessary operation. 

What is a Sentinel Lymph Node?

The sentinel lymph node is the "guardian node" of a lymph node region. It is the first lymph node in a region that a melanoma will metastasise to. Detecting the sentinel lymph node relies on a very important anatomical feature of the lymphatic system, this being that the water channel from a particular area of the skin always drains to the same lymph gland. The skin can be likened to a quilt with lots of individual pieces connected together. Each piece of skin has its own lymphatic channel and this channel follows a set pathway to its specific lymph gland. So, water from a particular piece of the skin (and any bacteria or cancer cells carried with it) will always follow the same pathway and always end up being filtered by the same lymph gland. Lymph glands are able to sieve out, trap and hold onto tumour cells. The immune cells in the lymph gland then attack the cancer cell (or bacteria) and try and kill it. If successful, one's cancer may be cured. If not, the cancer cells will continue to multiply within the lymph gland ultimately spreading to other lymph glands and via the blood stream to organs.

How do You Identify the Sentinel Lymph Node?

The sentinel lymph node is identified by injecting a mildly radioactive dye into the skin around the original biopsy site of the melanoma. The dye is absorbed into the lymphatic channels and then travels along the channels to the sentinel lymph node where it becomes trapped and concentrated. Screening with a gamma camera (which can detect radiation) then allows one to identify where the sentinel lymph gland is. This procedure is performed by a nuclear physician and occurs prior to going to theatre (operating room), usually the previous afternoon or on the morning of surgery. It takes about an hour and a half for the screening to be done.

How is the Sentinel Lymph Node Removed?

Removal of the sentinel lymph node is done in theatre under a general anaesthetic. To assist with the identification of the sentinel lymph node, blue dye is injected into the melanoma biopsy site once the patient has been anaesthetised. The blue dye is rapidly carried to the sentinel lymph node and becomes concentrated there. A handheld Geiger counter is then held against the skin and used to identify where the greatest concentration of radiation is coming from. A short incision (cut) is made directly over this point and, using the Geiger counter to identify the area of greatest radiation, one carefully works one's way inwards to find the sentinel lymph node. If one has identified the correct node, it will appear blue in colour and have a high radioactive reading. The node is removed and sent for analysis in the pathology laboratory.

Do I Need a Sentinel Lymph Node Biopsy?

A sentinel lymph node biopsy is recommended where there is a significant risk of metastasis to the lymph nodes. Patients with a 15 to 20% risk (or higher) of lymph node metastasis are candidates. This means that any patient who has a melanoma which is thicker than 0.8 mm or where the primary melanoma was ulcerated (made a sore or scab) or had a significant number of mitoses should be offered a sentinel lymph node biopsy.