There are four main subtypes of melanoma: superficial spreading melanoma, nodular melanoma, lentigomaligna melanoma, and acrallentiginous melanoma. Rarer subtypes of melanoma include nevoid melanoma, desmoplastic melanoma, clear cell sarcoma, and solitary dermal melanoma.
Superficial spreading melanoma accounts for the majority of melanomas comprising 50-80% of all melanoma diagnoses. As its name suggests, it is a form of melanoma in which only the superficial layer of the skin is affected and the melanoma has only grown horizontally along the skin surface and vertical (deeper) growth has not yet occurred. It is most frequently seen on those areas of skin exposed to the sun such as the back in men and the lower limbs in women, however it may occur on any region of the body. These melanomas arise de novo yet can also occur within a pre existing mole.
When examined, a superficial spreading melanoma appears multicolored with a well definedand often irregular border. Typical presentations include lesions that have multiple shades of tan, brown, black, grey, purple, pink, and, rarely, blue areas and may possibly have small or localised whitish areas (hypopigmentation).
20 – 30% of diagnosed melanomas are of the Nodular melanoma type. This type of melanoma is characterized by the early onset of growth in a vertical direction, meaning cancer cells are seen in the deeper layers of the skin at an earlier time frame. Nodular melanoma is more common in men, and usually found on the trunk in men and legs in women.On examination, they appear as a uniformly dark brown, black, or blue-black pigmented lesions.
Lentigomaligna melanoma is seen most often in the elderly population, particularly those with a history of sun-damaged skin. This melanoma has a predilection for those areas of the skin regularly exposed to the sun such as the temples, nose, forehead, neck, and forearms.
On examination, lentigomaligna melanoma commonly presents as a slowly enlarging patch that is flat with variable pigment that may be tan, brown, and black in appearance. Additionally, the tumor is stereotypically asymmetrical with irregular borders. Lentigomaligna, while often small initially, can reach several inches in diameter if left untreated. This melanoma may take many years to reach the invasive stage of growth, however, immediate treatment is required if this melanoma is diagnosed.
Acrallentiginous melanoma is not a common melanoma seen in Brisbane and is most often reported in African American populations and those with darker complexions. It is the rarest subtype of melanoma, accounting for less than 5% of all melanomas.These melanomas are characteristically found on hairless areas of the body such as the nail bed, the palms and the underside of the feet.
On examination, an acrallentiginous melanoma regularly develops as a unevenly colored patch, usually brown or black, that has an irregular border and increases in size with time.The surface may feel raised to touch particularly when the tumor grows deeper into the skin and becomes invasive.
When this melanoma occurs in the nail bed it often appears as a brown or black longitudinal line extending from the cuticle to the tip of the nail.