Question:

A 52-year old woman complained of a nodular growth at a "mole" on her buttock for six months. The lesion bleeds on scratching and catching clothes. She enjoys good past health.

Malignant melanoma is a malignant tumour arising from the epidermal melanocytes. It can arise de novo or from a pre-existing melanocytic naevus. The clinical features of melanoma is irregularly shaped lesion of variegated pigmentation. There can be nodular growth. Ulceration and bleeding are not uncommon. There are several subtypes of melanoma; superficial spreading, nodular, acral lentiginous, subungual, lentigo maligna melanoma. There are two systems proposed by the US and UK to aid clinical diagnosis of malignant melanoma. The American ABCD (A=asymmetry; B=irregular border; C=irregular colour; D=diameter over 1 cm). The Glasgow 7-point checklist which includes three major features (change in size, change in shape and change in colour) and four minor features (diameter over 6 mm, inflammation, oozing or bleeding, mild itch or alteration in sensation). The prognosis depends on the staging of the tumour and also the pathology of the lesion. The Breslow's tumour thickness and the Clark's level of invasion into the dermis are well-known pathological prognostic indicators.

Seborrhoeic keratosis is a benign skin tumour, mainly occurs in the elderly. It is characterised by pigmented warty plaque with "stuck on" appearance on the skin. Melanocytic naevus can be congenital or acquired. It is distinguished from melanoma by its regular and symmetrical appearance and homogenous pigmentation. Lentigo maligna melanoma is a subtype of malignant melanoma which mostly occurs on the upper cheek, temple and forehead. It presents as flat, pigmented lesion of irregular shape and colour.