Melanoma

Melanoma is the most lethal form of skin cancer. We as South Africans are particularly at risk because of our excellent weather and outdoor lifestyle. These cancerous growths develop when DNA damage occurs in skin cells (most often caused by ultraviolet radiation from sun exposure or tanning beds). This triggers genetic mutations that cause the skin cells to multiply rapidly and form malignant tumours. These tumours originate in the pigment-producing melanocytes in the basal layer of the epidermis (the upper layer of the skin) and mostly resemble the appearance of moles. Most melanomas are black or brown, but they can also be pink, red, purple, blue or white.

Melanoma warning signs:

You should examine your skin from head to toe at least once a month to look for any new moles or changes in existing moles. Lesions that itch, bleed or do not heal are also danger signs. The following melanoma characteristics are important to recognize when evaluating moles for the presence of melanomas (ABCDE!):

• Asymmetry:
  Asymmetrical moles are more likely to be melanomas.
• Borders:
  Uneven borders or borders with raised or scalloped edges are suspicious.
• Colour:
  Melanomas are more likely to be multiple shades of brown, but can also be pink, white, red or blue.
• Diameter:
  Melanomas are usually larger in size with a diameter more than 6 mm raising suspicion.
• Evolving
  Any recent change in a mole is suspicious.

Melanomas may develop anywhere on your body but often develop in areas that have been exposed to the sun, such as your back, legs, arms and face. Melanomas may also develop in areas that are not exposed to the sun, such as the soles of your feet, the palms of your hands and fingernail beds. These are categorized as hidden melanomas and are more common in people with dark skin.

Melanomas don’t always start as a mole; they may develop on normal-looking skin.

Risk factors for developing melanoma are as follows:

• Increased sun exposure, especially with episodes of sunburn
• Presence of moles, the more moles you have, the higher the risk
• Skin type: the fairer the skin, the higher the risk
• Weakened immunity: patients with cancer, HIV, lymphoma or those undergoing chemotherapy are at increased risk of melanoma.
• Personal history of skin cancer
• Family history: 10% of patient with the disease will have a family member with a history of melanoma.
• A change on your existing mole
• Development of a new, pigmented or unusual-looking growth on your skin

If melanoma is detected and treated early, the chance of cure is excellent. If it is detected after it has spread to other organs, it can be very difficult to treat and may be fatal.

There are 4 recognized types of melanoma:

Three of them occupy the top layers of the skin and only occasionally become invasive, whereas the fourth type is invasive from the start. Invasive melanomas carry a poorer prognosis.

• Superficial spreading melanoma:
  Superficial spreading melanoma is the most common type of melanoma which normally appears on the trunk or limbs. It will remain in the superficial layers of the skin for a fairly long time before it becomes invasive. It can occur in a previously benign mole.
• Lentigo maligna melanoma:
  This type of melanoma is less common and occurs more in elderly people, in chronically sun-damaged areas such as the face, arms and upper torso.
• Acral lentiginous melanoma:
  This is the rarest type of melanoma. It spreads superficially before invading deeper skin layers. It is however different in that the lesions usually appear as brown or black discolourations under the nails or on the palms of the hands or soles of the feet.
• Nodular melanoma:
  This type is usually invasive at the time of diagnosis already. Nodular melanoma may be recognized as a palpable lump and is usually black in colour, but can also be blue, grey, white, brown, tan, red or skin colour. This is the most aggressive form of melanoma and usually develops on the trunk, head or neck.

How are melanomas treated?

Once the diagnosis of melanoma is considered, it needs to be confirmed/excluded by performing a surgical biopsy. The lesion is excised with a 1mm margin and sent for histological evaluation. The histology will confirm the diagnosis; determine the type of melanoma and the depth of infiltration. The depth of infiltration is the most important as this will determine the prognosis to a large extent, and will also determine with what size of margin the biopsy scar needs to be re-excised. This is necessary to decrease the chance of a local recurrence:

• For ‘in situ’ melanoma (cancer confined to the uppermost layer of the skin) a margin of 0.5 – 1cm is sufficient when excising the scar.
• For a tumour depth of 1mm, the margins are extended to 1cm.
• For a melanoma of 1 – 2mm thick a margin of 1-2cm is taken.
• If the melanoma is >2mm thick a margin of 2cm is sufficient.
• If the tumour is 1mm thick or more, the patient also needs a sentinel lymph node biopsy.

Normally cell growth occurs via an orderly process With a sentinel lymph node biopsy, a radioactive substance is injected into the tumour site. The first lymph node that drains the area of the melanoma (i.e. a groin lymph node if the lesion is on the skin of the leg) is identified and removed. If there is cancer in this node, all the lymph nodes of the groin area are removed; if it is clear of cancer, no further surgery is done.

Patients with deep primary tumours (>4mm thick) or those with the lymph-node positive disease are considered to have a high risk of systemic/recurrent disease and would qualify for some form of adjuvant therapy such as chemotherapy, immunotherapy or radiation therapy. Interferon alfa is approved for adjuvant treatment after excision in patients who are free of disease but are at high risk for recurrence.

Conventional chemotherapy, radiotherapy, granulocyte-macrophage colony-stimulating factor (GM-CSF) and immunotherapy (vemurafenib) all have a role to play in the adjuvant setting.