SeminarNon-melanoma skin cancer
Introduction
The term non-melanoma skin cancers (or keratinocyte carcinomas) encompasses cutaneous lymphomas, adnexal tumours, Merkel-cell carcinomas, and other rare primary cutaneous neoplasms, but is mainly used to define basal-cell carcinomas and squamous-cell carcinomas. Grouping of these two carcinomas under a common umbrella term poses challenges, because clear differences exist in their aetiopathogenesis, clinical course, and management strategies. Non-melanoma skin cancers are the most common human cancers, and despite growing public awareness of the harmful effects of sun exposure, incidence continues to rise.1, 2 A 3–8% yearly increase in incidence of non-melanoma skin cancer has been reported since 1960 worldwide.3, 4 Incidence of basal-cell carcinoma alone is increasing by 10% per year worldwide, suggesting that prevalence of this tumour will soon equal that of all other cancers combined.5 Furthermore, an estimated 40–50% of patients with a primary carcinoma will develop at least one or more further basal-cell carcinomas within 5 years. The estimated incidence of non-melanoma skin cancer in the USA is more than 1 000 000 cases per year, of which roughly 20–30% are of squamous-cell carcinoma.6
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Epidemiology
Unfortunately, because of variation between registries in data capture, recording, and processing for skin-cancer registration, accurate figures for incidence of non-melanoma skin cancer in the UK are difficult to obtain.7 More than 76 000 new cases of non-melanoma skin cancer were registered in the UK in 2005, but the actual incidence is estimated to be at least 100 000 cases per year.8 Results of a Welsh study9 showed that the crude incidence of non-melanoma skin cancer increased from 173·5
Pathogenesis
UVB radiation causes direct damage to DNA and RNA by inducing covalent bond formation between adjacent pyrimidines, leading to generation of mutagenic photoproducts such as cyclopyrimidine dimers (TT) and pyrimidine-pyrimidine (6-4) adducts.25 UVA is less mutagenic than is UVB, and causes indirect DNA damage via a photo-oxidative-stress-mediated mechanism, resulting in formation of reactive oxygen species, which interact with lipids, proteins, and DNA to generate intermediates that combine with
Diagnosis
Early basal-cell carcinomas are usually small, translucent, or pearly, with raised telangiectatic edges. Roughly 80% of all basal-cell carcinomas occur on the head and neck, and clinical diagnosis is fairly straightforward.72 In addition to the classic rodent ulcer with an indurated edge and ulcerated centre, nodular or cystic, superficial, morphoeic, and pigmented basal-cell carcinomas are other common subtypes (figure 3). 10–40% of basal-cell carcinomas contain a mixed pattern of two or more
Prognosis and staging
Non-melanoma skin cancers, especially basal-cell carcinomas, have low metastatic potential and are associated with low mortality. The likelihood of metastases and recurrence of squamous-cell and basal-cell carcinoma depends on several prognostic indicators (table 4).86, 89, 90, 91 These indicators draw attention to the importance of a detailed pathological description, since individual lesion and host characteristics have to be taken into account when determining the prognosis of non-melanoma
Management
The British Association of Dermatologists has issued guidelines for management of non-melanoma skin cancers.86, 98 Interventions for management of basal-cell carcinomas in immunocompetent patients and prevention of non-melanoma skin cancers in high-risk groups have been systematically reviewed.99, 100 Routine use of sunscreen might prevent squamous-cell carcinoma, but is of unproven benefit in basal-cell carcinoma.101 Several government and charitable organisations have launched prevention
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