Melanoma

Melanoma is a rare type of skin cancer which affects all age groups. Although melanoma is the major cause of skin cancer mortality, it is usually curable if detected and treated at an early stage (Scottish Intercollegiate Guidelines Network [SIGN], 2009).

What is melanoma?
Melanoma occurs after the malignant transformation of melanocytes (Barnhill et al., 1993). The melanocyte is a skin cell, which is found in the epidermis. Its most important physiological function is to produce melanin, one of the pigments responsible for skin colour. This helps to protect the skin from damage caused by UV radiation from the sun. Most melanocytes are found in the skin and it is for this reason that most melanomas are known as cutaneous melanomas (see Figure 11.5).


At first melanomas grow horizontally. The basement membrane, a barrier separating the epidermis from the dermis, acts as a mechanical barrier, preventing the melanoma from invading deeper into the skin. Early stages of melanoma that are limited to the epidermis are called melanoma in situ and are curable. If the melanoma cells grow vertically through the basement membrane to the dermis, it is known as an ‘invasive’ melanoma. The depth that the melanoma grows into the skin provides important prognostic information. The measurement, known as the Breslow thickness, is taken from the granular layer of the epidermis to the base of the tumour (Roberts et al., 2002) and is measured in millimetres with a small ruler called a micrometer (see Figure 11.6). The greater the Breslow thickness, the greater the chance the cancer may spread to other areas of the body via the lymphatic or blood stream.

Figure 11.6 Breslow thickness. (Source: Reprinted from Graham-Brown and Burns, 2006.)