SPREAD OF MELANOMA
I HAVE A MELANOMA. WHAT HAPPENS NOW?
After a melanoma is diagnosed, the next step is to determine the clinical stage or extent of disease spread. Accurate staging is important to determine the most appropriate treatment. There are several techniques for investigating the spread of melanoma and these are discussed below but first the factors that influence the risk of spread are discussed.
RISK OF SPREAD
DOES THE DEPTH OF A MELANOMA INCREASE 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 millimeters 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 metastasis.
Other major features of a primary melanoma that determine the risk of spread are whether it it had formed a sore (ulceration) and the number of actively dividing cells (mitotic cells) seen per field under the microscope.
WHERE DO MELANOMAS SPREAD TO?
If a melanoma metastasizes, 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. In a significant percentage of patients spread will remain confined to the lymph glands for a period of time. If one can identify these patients and remove the glands that have been affected (and all the other glands in the surrounding area) there is a good chance of cure. If melanoma has spread from the glands via the blood stream to distant organs then a cure may not be possible. 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?
The likelihood that spread to the lymph glands has occurred is mainly determined by the Breslow depth of the primary melanoma. There is a threshold Breslow depth of around 1 mm where the risk of lymphatic spread rises significantly. Melanomas thinner than 1 mm have a low (5%) risk of lymph node spread while those thicker than 1 mm have at least a 15 to 20% chance of spread. Ulceration (the melanoma has formed a sore) and a high mitotic count also increase the risk of spread which means that melanomas thinner than 1 mm with these features also have a 15 to 20% risk of lymph node metastases.
WHAT DOES IT MEAN IF THE LYMPH NODES ARE INVOLVED?
The most significant determinant of prognosis in melanoma is the status of the lymph nodes. If there has been no metastasis (spread) 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.
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 new 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 palpated (felt) 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 WHY DO I NEED TO HAVE A SCAN?
Scans are then done to assess whether the melanoma has metastasized (spread). The complexity (and expense) of the scans is determined by the risk of spread.
If there is a low risk of spread (melanoma thinner than 1 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 commonest organ that melanomas spread to and it's cheap, easy and accurate to exclude spread with an X-ray of the chest.
If the melanoma has penetrated more deeply (melanoma thicker than 1 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.
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.
If an enlarged lymph gland is detected on clinical examination then an ultrasound scan of the lymph nodes is requested. An ultrasound 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. 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 usually requested if spread to lymph glands has been detected on sentinel lymph node biopsy (see below) to more accurately assess whether spread has occurred to any of the internal organs. NB:No type of scan can detect microscopic disease. If a scan is clear in someone who has had a melanoma it does not exclude microscopic spread. Unfortunately, microscopic deposits of melanoma can continue to grow and it is therefore necessary to continue regular follow-ups and scans.
HOW DO I KNOW IF THE 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 pathology then a needle aspiration (withdraw fluid) 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. This would normally be done at the same time as the wide local excision. 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.
WILL A BLOOD TEST RESULT SHOW IF I HAVE A NEW MELANOMA OR NOT?
Blood tests are available which can be used to screen for melanoma metastases. A liver enzyme, Lactate Dehydrogenase (LD) and a protein marker on melanoma cells (S100B) can be measured in the blood. A rapid rise in the baseline level of these blood markers may signify a metastasis in an organ and necessitate screening with a PET-CT scan. In our clinic, these blood markers are only measured in patients who have had metastases removed from the lymph glands or an internal organ, and have no evidence of any further spread on PET-CT scan.
SENTINEL LYMPH NODE BIOPSY
IS IT WORTHWHILE TO HAVE 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 lymph gland within a lymph node region (such as the groin, neck or axilla) that has the greatest likelihood of harboring a metastasis. 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 with in that region have melanoma metastases and no further surgery is required.
WHAT IS A SENTINEL LYMPH NODE?
Sentinel lymph node biopsy 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 the same path 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 trap and hold onto tumour cells for a period of time before spread either occurs to a higher lymph node or to the blood stream. If one can identify and remove the offending lymph glands before spread in the blood has occurred then a cure is possible.
HOW DO YOU FIND 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 follows the lymphatic 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.
HOW IS THE SENTINEL LYMPH NODE REMOVED?
Removal of the sentinel lymph gland is done in theatre under a general anaesthetic and is performed prior to doing the wide local excision (see below). To assist in the identification of the sentinel lymph node, blue dye is injected into the biopsy site once the patient has been anaesthetised. This rapidly gets carried to the sentinel node and is concentrated there. A hand held 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 over this point and, using the Geiger counter to identify the source of greatest radiation, one carefully works one's way inwards to reveal the sentinel node. If one has identified the correct node it will appear blue in colour and have a high radioactive reading. The gland is removed and sent for analysis in the path lab.
WHO NEEDS A SENTINEL LYMPH NODE BIOPSY?
A sentinel lymph node biopsy is recommended where there is a significant risk of metastasis to the lymph glands. Patients with a 15 to 20% risk of lymph node metastasis are candidates. This means that any patient who has a melanoma which is thicker than 1 mm or where the primary melanoma was ulcerated or had a significant number of mitoses should be offered a sentinel node biopsy. Younger male patients with thin melanomas (less than 1 mm thick) on the trunk (chest, back, abdomen) are also candidates even if there are no additional sinister features of the primary melanoma.