Melanocytes originate in the neural crest of the embryo and migrate widely during development to locations such as the basal layer of the epidermis and the uveal tract. As a result, malignant melanoma (MM) can affect sites other than the skin, including the central nervous system (e.g. meninges and uveal tract) and the aerodigestive and genitourinary tracts (e.g. nasopharynx, oral cavity and vagina). Cutaneous melanoma has one of the fastest rising cancer incidences worldwide. In the UK it is the fifth commonest cancer and the second commonest cancer in the 15–34 year age group, with about 27% of cases occurring below the age of 50 (http://www.cancerresearchuk.org/, accessed February 2015).
Mortality rates have also increased over time, but less so than the increase in incidence because of improvements in the chance of survival from melanoma. Mortality rates appear to have stabilised in some countries, most notably Australia. A shift to proportionately more in situ and thin melanomas being diagnosed in the same period suggests that this reduction in mortality may be due to earlier detection (Coory et al., 2006).
This chapter focuses on cutaneous melanoma, but will also cover some of the main features of the rarer subtypes such as mucosal and ocular melanoma.
Types of cutaneous melanoma
The main clinicopathological varieties of cutaneous MM are superficial spreading, nodular, acral lentiginous and lentigo maligna melanoma.
Incidence and epidemiology
The annual age-standardised disease incidence of cutaneous melanoma in the UK is 17 per 100,000. Approximately 11,500 new cases are diagnosed per year in England and Wales, comprising 4% of all new cancer cases. Around 2000 deaths from melanoma occur annually in the UK (from Cancer Research UK, http://www.cancerresearchuk.org/, accessed February 2014).
The incidence of cutaneous melanoma has continued to rise worldwide for the last 40 years. The annual increase varies between populations, but in general has been in the order of 3–7% per year for fair-skinned Caucasian people. Some of this increase may be due to increased surveillance and therefore earlier detection, as well as changes in diagnostic criteria. However, most of the increase is considered real, and linked to changes in lifestyle resulting in excessive recreational exposure to sunlight (Lens and Dawes, 2004).