While it is difficult to assess the total number of cases of nonmelanoma skin cancers given the lack of population-based registries, it is estimated that over five million basal and squamous cell carcinomas are diagnosed each year. Of these, approximately two in ten are squamous cell carcinomas, which we will focus on here given their greater propensity to be more aggressive than basal cell carcinomas. The overwhelming majority of squamous cell carcinomas (approximately 80%) develop in the head and neck. This is likely related to UV light exposure, which is one of the strongest risk factors for the development of nonmelanoma skin cancers. Other risk factors include previous radiation exposure, actinic keratoses, immunosuppression, previous scars or burns, and disorders such as xeroderma pigmentosum, epidermolysis bullosa, and pansclerotic morphea of childhood.

Given that most patients with cutaneous squamous cell carcinoma present with primaries on the head and neck, there is little data about the frequency and management of inguinal lymph node involvement from perineal or lower extremity primaries. Lymph node metastasis is often associated with adverse pathologic findings such as lymphovascular invasion, poor differentiation, and perineural invasion. High-risk lesions, defined as primaries greater than 2 cm on the extremities with adverse pathologic findings or in the setting of immunosuppression, tend to have higher rates of lymph node and distant metastases. Patients with nodal metastases have expected 10-year survival of less than 20% [7]. In general, rates of nodal involvement are low, but early detection and treatment may significantly alter the prognosis of patients with lymph node metastases.

Merkel cell carcinoma (MCC ) is a rare neuroendocrine cancer of the skin with a historically poor prognosis. It is one of the least common types of skin cancer, with an estimated 1500 case diagnoses per year. MCC is essentially a disease of older whites, with two-thirds of patients over the age of 70 and nine out of ten patients being white. Risk factors include extensive sun exposure, older age, and immunosuppression. Immunosuppressed patients that develop MCC tend to be much younger (approximately 50% younger than 50 years old) than immunocompetent patients with MCC. A novel polyomavirus has been identified in a majority of cases of MCC, but a causal link between this virus and the development of MCC has not been established [8].

Approximately 15% of patients with MCC present with primary lesions on the lower extremity and 27% present with lymph node involvement [9]. Nodal involvement is associated with a decrease in 5-year survival from 64% with local disease to approximately 39%. Nodal disease is detected in the sentinel lymph node in approximately one-third of patients without clinically detectable lymph node metastasis. Patients with pathologically negative sentinel lymph nodes appear to have a survival advantage compared to patients that undergo only clinical nodal evaluation, which confirms the utility of sentinel lymph node biopsy.