Malignant melanoma:

Malignant melanoma is the most serious form of skin cancer as metastases can occur early and it causes a number of deaths even in young people. As with other types of skin cancer the incidence is continuing to increase, probably because of excessive exposure to sunlight. The history of childhood sun exposure and intermittent sun exposure appears to play a role in the development of malignant melanoma. Other risk factors include atypical mole syndrome, giant congenital melanocytic naevi, lentigo maligna and a positive family history of malignant melanoma. Malignant melanoma is commoner in later life; young adults are also affected. The tumour suppressor gene p16 (on chromosome 9p) is frequently mutated or deleted in melanoma cell lines and its role in atypical mole syndrome/familial melanoma is currently under investigation.
Diagnosis of melanoma is not always easy but the clinical signs listed in Table 23.11 help distinguish malignant from benign moles. Examination with a dermatoscope can further help in detecting malignant lesions.
Four clinical types exist:
Lentigo maligna melanoma is where a patch of lentigo maligna develops a papule or nodule signalling invasive tumour.
Superficial spreading malignant melanoma is a large flat irregularly pigmented lesion which grows laterally before vertical invasion develops.
Nodular malignant melanoma (Fig. 23.34) is the most aggressive type. It presents as a rapidly growing pigmented nodule which bleeds or ulcerates. Rarely they are amelanotic (non-pigmented) and can mimic pyogenic granuloma.
Acral lentiginous malignant melanoma arises as pigmented lesions on the palm, sole or under the nail and it usually presents late.





Integration link: Melanoma - subtypes

Taken from General & Systematic Pathology 4e




Table 23-11. Clinical criteria for the diagnosis of malignant melanoma
ABCDE criteria (USA)
Asymmetry of mole
Border irregularity
Colour variegation
Diameter > 6 mm
Elevation
The Glasgow 7-point checklist
Major criteria Change in size
Change in shape
Change in colour
Minor criteria Diameter more than 6 mm
Inflammation
Oozing or bleeding
Mild itch or altered sensation



Figure 23.34 Nodular malignant melanoma.
Treatment
This consists of urgent wide excision (2 cm margin) of the lesion. Histological analysis will determine the depth of invasion ('Clark's level') and the thickness of the tumour ('Breslow thickness'). These two factors are significant in predicting prognosis and 5-year survival rates: 96% for local lesions, 60% for regional spread and 14% for distant metastases. For localized melanomas the thickness and presence or absence of ulceration are the strongest independent predictors of outcome. Excision and histology interpretation should only be done by experts to ensure optimum treatment and assessment of prognosis. Sentinel node biopsy for patients with thicker lesions is required for predicting prognosis: 15% will be positive without clinical lymphadenopathy. Metastatic disease is best managed by an oncologist with a multidisciplinary team and can involve surgery to lymph nodes, radiotherapy, immunotherapy and chemotherapy. Initial optimism for high-dose alpha-interferon therapy in advanced disease has recently been challenged with a systematic review suggesting no clear benefit.
The role of governments and medical personnel in public health education to discourage sunbathing and to use sunscreens is of the utmost importance in skin cancer prevention.