Squamous cell carcinoma (SCC) is the second most common form of skin cancer after basal cell carcinoma (BCC). In 1775, Percival Pott published "Chirurgical Observations Relative to the Cancer of the Scrotum" in which he detailed the primary development and metastatic progression of lesions involving the scrotum of chimney sweeps.1 The publication was the first to identify a carcinogen and its occupational link to malignancy. The first detailed clinical description of BCC was by Arthur Jacob half a century later.1 In 1828, Jean-Nicolas Marjolin described malignant transformation within traumatic scars, while it is reported that in 1860, Heurteux first described an instance of carcinoma in a burn scar, a condition that has eponymously come to be known as Marjolin’s ulcer.1
Squamous cell carcinoma usually occurs on skin affected by chronic exposure to sunlight. It is less common than BCC, occurring approximately four times less frequently. The incidence of SCC has risen more sharply than that of BCC in recent decades and this change has been attributed to increased cumulative UV exposure.2 Globally, the highest incidence of SCC is in Australia where the rate is 387 per 100,000 person-years, while the lowest recorded rates are in parts of Africa.3,4 SCC rates have been shown to vary with latitude, with higher rates documented toward the equator.3 There is an overall gender disparity of approximately 2:1, with lesions affecting men more frequently than women.3 However, when a young population (below the age of 40) is analyzed, there is a similar incidence in men and women.5 SCC is rare below the age of 25, with less than 1% of all lesions occurring in this age group.6 The incidence of SCC rises dramatically from age 50 in Australia and the cumulative risk of developing an SCC by age 70 is reported to be 34% and 22% for men and women, respectively.3,6
Anatomically, SCC most commonly occurs in the head and neck region, with frequent involvement of the nose, ears, and cheeks.7 It is also common for SCC to occur on the upper limbs, with frequent involvement of the hands and to a slightly lesser extent the forearm. The relative density of SCC in parts of the body such as the trunk and buttocks, which are typically protected from exposure to solar radiation, is lower. However, variations in sartorial, cultural, and occupational practices between the sexes are reflected in the anatomical distribution of lesions.7
Squamous cell carcinomas can metastasize and their propensity for metastatic spread is widely reported in the literature. The reported rate of metastasis ranges between 0.5% and 16%.8 Regional lymph nodes are the most common site for metastatic spread; however, distant disease involving bones, lung, and other visceral structures occur in 5% to 10% of patients with metastatic disease.