Non-melanoma skin cancer (NMSC) is by far the most frequently diagnosed cancer. The most common NMSCs are basal cell carcinoma (BCC) and spinocellular carcinoma (SCC), accounting for 70% and 25% of NMSCs, respectively, although skin cancers can arise from any skin host cell. NMSCs exhibit different behavior, growth, and metastatic ability; however, both BCC and SCC have a good prognosis, especially when detected in their early stages. BCC contributes minimally to the NMSC mortality rate (MR). In fact, metastatic BCC shows an incidence of 1 case per 14 000 000 and 2 patients per 14 000 000 dying of locally advanced BCC. Therefore, an MR of 0.02 per 10,000 can be expected. On the other hand, SCC shows a variable metastatic rate of 0.1-9.9% and accounts for approximately 75% of deaths due to NMSC.
BCC is characterized by cells resembling epidermal basal cells and is the least aggressive NMSC. In fact, BCC exhibits a low degree of malignancy despite the ability for local invasion, tissue destruction, recurrence, and limited potential for metastasis. Individual risk factors for BCC include sex, age, immunosuppression, genetic disease (e.g., Gorlin-Goltz syndrome), and Fitzpatrick skin types I and II. However, ultraviolet (UV) radiation plays the most important role in the pathogenesis of BCC, although the relationship between UV radiation and the development of BCC remains highly controversial. BCC develops primarily on sun-exposed skin. In fact, BCC is rarely found on palmoplantar surfaces and never appears on the mucosa.
SCC is characterized by atypical proliferation of invasive squamous cells, which may metastasize. In addition, SCCs show considerable potential for recurrence, which depends on tumor size, degree of histologic differentiation, depth of the lesion, perineural invasion, the patient's immune system, and anatomic location. Several risk factors have been reported in patients with SCC, including Fitzpatrick skin types I and II, outdoor activity, tanning beds, types 16, 18, and 31 of the human papillomavirus (HPV) and genetically inherited skin diseases, such as albinism, xeroderma pigmentosum, and epidermodysplasia verruciformis. However, the most important risk factor is UV radiation and sunlight.