Melanoma is a unique type of cancer normally arising in the skin arising from melanocytes. Melanocytes make a cell pigment melanin; this is present to protect the skin from ultraviolet damage. A melanoma may begin in a mole but can also begin in other pigmented tissues such as in the eye or the intestines.
Incidence of melanoma
Malignant melanoma is a relatively uncommon cancer in the UK where it comprises only 1% of cancers and only 1200 deaths per year; however, there are some data to suggest that the incidence is rising. By contrast, the incidence in Queensland, Australia, where a Caucasian population are heavily exposed to sunlight, is 5 per 1,000 of the population indicating the breadth of incidence of this highly fatal cancer across the globe. Whilst the incidence of melanoma is highest in Australia, there is good evidence that the incidence in Europe and America is rising. In the European population, the increase in incidence has been linked to a greater opportunity for foreign travel and sunbathing holidays. This increased chance of taking holidays in the sun may in part explain why there is a higher incidence of the disease in higher social classes In America, the Surveillance, Epidemiology and End Results (SEER) study showed a steady increase in incidence of cutaneous melanoma at various latitudes, again reinforcing the sunshine exposure risk factor. The disease is more common in women by a factor of approximately twofold - in Europe and America (but not in Australia). Also, there is a tendency for melanoma to occur on the trunk in men and extremities in women; facial melanoma tends to be a disease of the elderly. Mucosal melanoma is relatively more common in dark skinned races, in whom the incidence of skin melanoma is less frequent.
Symptoms of melanoma
The most characteristic feature associated with a melanoma is the black colour of the skin lesion. Whilst some malignant melanomas arise from benign naevi (‘moles’) the majority arise from normal skin. The development of a black skin lesion must never be ignored and the changes within a pre-existing skin lesion, particularly of its size, shape and colour should all alert the patient and doctors. The development of bleeding, crusting and a change in sensation or inflammation in a skin lesion merits further assessment.
A proportion of patients may present with signs or symptoms of disseminated melanoma. These may include the development of lymph nodes or skin nodules; pain from metastases, weight loss or neurological symptoms if there has been spread to the brain or spine.
There are several clinically recognised types of presentation: the first is the superficial spreading type of melanoma (up to 2/3 of cases) where a flat, coloured skin lesion progressively grows irregularly in the skin, typically on the limbs.
The nodular melanoma has more substance to it, is frequently faster growing and tends to be a rounder nodular skin lump, such nodular cases account for up to 20% of all cases.
The rarer types of melanoma are the lentigo maligna melanoma which is a very slow growing flat skin lesion growing on the face of typically elderly and female patients and the acral type which is found on the palms and soles and mucosal membranes and typically encountered in Asian and black peoples.
Treatment of melanoma
In most patients, surgery is required to remove (or excise) the entire tumour. Generally, one to two centimetres of normal skin surrounding the lesion must also be removed. Occasionally, skin grafting may be necessary to promote healing and replace skin that has been removed.
If an enlarged lymph node (or gland) is present, it may be biopsied at the time of the wide local excision. Even if enlarged lymph nodes cannot be detected, the lymph nodes may be evaluated during or after the surgical removal of the melanoma.
In the majority of cases, enlarged lymph nodes are not visible, and the only way to determine if they are affected is to take a sample of the lymph node during surgery. The sample is then examined under a microscope to determine if abnormal cells are present. This is typically accomplished with a surgical technique known as sentinel lymph node (SLN) biopsy.
The sentinel lymph node (SLN) technique is based upon the theory that when tumour cells migrate, they spread to one or a few lymph nodes before involving other nodes. Further, these nodes can be identified by injecting a blue dye or radioactive material around the primary tumour before the wide local excision, and then searching for the node that has taken up the dye or the radioactive tracer at the time of surgery.
SLN biopsy has become the standard technique for assessing the status of regional lymph nodes and is recommended for staging of most patients with newly diagnosed primary melanomas. However, patients whose melanomas are less than 1 mm in thickness (thin melanomas) may not require SLN, since the likelihood of tumour spread to the regional lymph nodes is less than 10 percent.
In contrast, SLN biopsy may be advised for thin melanomas with other high-risk features, such as ulceration, Clark's level IV or V (the tumour has invaded deeper levels of the skin), or if there are significant areas of regression (spontaneous loss of tumour cells).
Based upon the pathologic disease stage, the optimal treatment is chosen. For patients with localized disease who have no evidence of distant metastases, the goals of treatment are:
- Complete surgical removal of the primary melanoma
- Evaluation of regional lymph nodes for evidence of tumour involvement
- Preventing further spread or disease recurrence
There are now data, not convincing to all but enough to have changed current, standard practice in the USA, to support the routine use of adjuvant alpha interferon (in high dosage and after surgery) for such high risk patients without metastatic disease to distant organs.
Alpha interferon adjuvant therapy in stage 2 and 3 disease is still under investigation, but at present it is the only
Treatment of advanced metastatic melanoma focuses on shrinking or eliminating the metastatic lesions, preventing further spread of the disease, and ensuring patient comfort. In most cases, it is not possible to completely eliminate the cancer. Depending on the location and extent of the metastases, treatment may involve the use of medical treatments (chemotherapy or immunotherapy), surgery, or radiation therapy.
Chemotherapy and immunotherapy treatments may be given alone or in combination. Most of these treatments must be given into a vein (intravenously) or injected under the skin, although a few can be given in pill form.
Each medication is given over a period of time, often several months or more, depending upon how the patient responds. Patients are monitored for signs of drug toxicity or side effects. Many side effects are temporary and can be managed so that patient discomfort is minimised.