Pathology Spotlight – Melanoma of the Skin

Our 14th Pathology Spotlight looks at a melanoma of the skin on a big toe. 

The specimen is a resected big toe with the right half of the toenail removed to reveal a melanoma, which is visible as an area of dark discolouration on the right side. According to the contemporary notes on the the specimen, the patient:-

previously had noticed a black spot at the lateral side of the nail. A portion of the nail was removed some days before amputation. The lateral half of the hallux (big toe) and of the nail-bed is replaced by a darkly pigmented irregular mass. Microscopic examination shows a melanoma’.

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Melanoma is an aggressive cancer occurring in tissue where there are cells that produce the body’s black pigment, melanin, such as the skin and parts of the eye. Melanoma is the commonest form of skin cancer and the 6th most common form of cancer generally. Its development is linked to exposure to ultra-violet (UV) solar radiation and the risk of developing melanoma is directly linked to the extent of sun exposure and sunburn; light-skinned people and those with fair or red hair are most at risk.  UV radiation causes sunburn at sufficiently high level, but, even at lower levels of exposure UV causes DNA damage which results in gene mutations. Mutations are the changes to DNA involved in converting a normal cell into a cancer cell. If a melanin producing cell – a melanocyte – becomes cancerous, then melanoma results. Age is an important risk factor and older people are far more likely to develop melanoma. This is because mutations accumulate with protracted sun damage over decades and also because aging is associated with a decrease in the ability to repair our DNA, an important mechanism in keeping cancer at bay.

Appearance of a regular mole (left) and a melanoma (right)  which is darker, larger and asymmetrical.

Melanoma is often first spotted as a mole that has changed and so any change in a mole regarding its size, shape, colour or symmetry, or if it becomes itchy or bleeds, should be sufficient for you to seek a check-up from your GP (image above). Melanoma arising under the toenail or fingernail, such as the one shown above, is rare and is only found in about 5% of all cases. Bob Marley the reggae musician died from this type of melanoma.

Featured image: Malignant Melanoma in situ. 



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