Squamous cell carcinoma: from precursor lesions to high-risk variants.

Cutaneous squamous cell carcinoma is second only to basal cell carcinoma in its incidence within our population. It is among the most common types of neoplasm afflicting the human race. Most cases are related to exposure to sunlight. This initial portion of the chapter will focus upon the biologic progression that results in the ultimate development of fully formed squamous cell carcinoma. The latter portion will focus upon the histologic features of squamous cell carcinoma, which may be potential prognostic indicators. While pathologists currently provide clinicians with information about many histologic features that may affect the outcome for patients with melanoma, there is little impetus for similar behavior on the part of pathologists when diagnosing squamous cell carcinomas. This is largely due to the relatively low metastasis rate for these tumors compared with melanomas; however, it may be possible for pathologists to separate out those squamous cell carcinomas with a higher chance for recurrence and metastasis. This chapter will examine many of these histologic features and propose a rationale for including this information in pathology reports.