Malignant Melanoma - the mole in the skin!

Malignant melanoma is the cancer of melanocytes which are mainly present in skin and are the cells forming pigment causing tanning of skin. Although it accounts for less than 5% of cancers (malignancies) of the skin generally it is responsible for over 75% of deaths related to skin malignancy, and is the commonest cancer in young adults (20–39 years) being the most likely cause of cancer-related death in this age group. So it should attract more public attention as it is a disease which could be identified at early stages and cured easily.

The incidence in white population in the UK and USA is doubling every 10 years. A higher number of cases have been reported in white people living near the equator than in temperate zones with the highest numbers (more than 40 per 100 000 per year) seen in white people living in Australia and New Zealand. Auckland of New Zealand is currently said to report the highest incidence per capita. This tumor is rare before puberty and in black people, Asians and Orientals. When it does occur in these races it is most often on the palms, soles or mucous membranes rather than the normal skin of the face and the body.

Ten to fifteen percent of melanomas are familial (occur in families where two or more first degree relatives have a melanoma); here molecular defects in genes like tumor suppressor gene and oncogenes have been linked to these melanomas and it may affect several members of a single family in association with atypical (dysplastic) nevi. Exposure to ultra violet rays (UVR) is the major causative factor for developing malignant melanoma and occurs most often in sun exposed skin particularly in white skinned nations. The risk of developing a malignant melanoma is highest in those with certain types of melanocytic nevi, like atypical nevi, congenital melanocytic nevi and many basal melanocytic nevi, but not all nevi cause malignancy. Only 10–20% of malignant melanomas are formed in pre-existing nevi, with the remaining majority arisingin previously normally pigmented skin. It is important to identify malignant forms from benign nevi.

There are several macroscopic (naked eye) features suggesting that a mole in the skin is likely to be a malignant melanoma rather than a benign melanocytic nevus.

1. Change in size – any adult nevus > 6 mm is suspect (for reference a lead pencil diameter is 7 mm) and anything changing to > 10mm is more likely to be malignant than benign

2. Shape

3. Colour

4. Surface irragularities (nodularity or ulceration)

5. Satellite lesions (discrete pigmented areas spreading away from the primary)

6. Tingling/itching/serosanguinous (pus like) discharge (usually late signs)

7. Blood supply: melanomas > 1 mm thick have a blood supply that can be found with a hand-held Doppler monitor, so ‘Doppler-positive’ pigmented lesions should be excised

 Eighty percent of invasive melanomas are preceded by a superficial and radial growing phase, shown clinically as the expansion of an irregularly pigmented macule (flat topped, well demarcated lesion, non-palpable lesion) or plaque (large, flat topped, elevated, palpable lesion). Most are multicolored mixtures of black, brown, blue, tan and pink. Their margins are irregular with projections and notches. Malignant cells are at first usually confined to the epidermis (superficial layer of skin) and uppermost dermis (deep layer of skin), but eventually invade more deeply and may metastasize.

There are four main types of malignant melanoma.

1. Superficial spreading melanoma is the most common type (70%) in Caucasians. Usually arise from pre-existing nevus. Its radial growth phase shows varied colours and is often palpable. A nodule coming up within such a plaque signifies deep dermal invasion and a poor prognosis.

2. Lentigo maligna melanoma occurs on the sun exposed skin of the elderly and is common in women accounting for 5% to 10% of malignant melanoma. An irregularly pigmented, irregularly shaped macule (flat topped, well demarcated, non-palpable lesion) may have been enlarging slowly for many years.

3. Acral lentiginous melanoma occurs on the palms and soles and, it is rare in white-skinned individuals (2–8%) but more common in the Afro-Caribbean, Hispanic and Asian populations(35–60%).

4. Nodular melanoma appears as a pigmented nodule and it is the most rapidly growing and aggressive type accounts to 15%.

A cancer is staged (stage of a cancer is a measure of severity and denotes the outcome) according to the thickness of the lesion and spreading to the deeper layers of skin, lymph node involvement and spread to distant organs like liver. There are several systems for staging of tumour. The most popular staging systems for melanoma are the TNM classification (Europe) and the American Joint Committee on Cancer Staging. Here the thickness of the lesion is important in staging i.e. the thicker is the lesion, higher becomes the stage and worse is the prognosis (outcome).

Surgical treatment: Surgical excision, with minimal delay, is required. An excision biopsy, with a 2-mm margin of clearance laterally, and down to the subcutaneous fat, is recommended for all suspicious lesions. If the histology confirms the diagnosis of malignant melanoma then wider excision, including the wound of the excision biopsy, should be performed as soon as possible. Elective regional lymph node dissection (known as a block dissection) may benefit patients with tumors of intermediate thickness.

Immunological treatment: Surgery cures most patients with early melanoma, but its effect on survival is less as the disease advances. Immunotherapy involves treating with immune mediators for certain malignancies. Here low dose α-interferon appears to improve the disease and may improve overall survival rates.

Chemotherapy: Although rarely curative, chemotherapy can be used to control the disease process in patients with severe disease.

Here what is most important to be noted is to identify suspicious lesions at the initial stages so that the treatment will be simple surgical removal and the prognosis is always better after treatment. It is said that at stage I the 5 year survival is nearly 85-95% (In cancers, the prognosis is expressed as survival; in malignant melanoma, it is expressed as 5 year survival). Therefore, presenting for early medical care in case of presence of a suspicious lesion should always be encouraged.