Contributor: Gordon K. Klintworth
A squamous cell carcinoma can arise in many parts of the body, including the lung [carcinoma - lung], skin [carcinoma - skin], nasopharynx [carcinoma - nasopharynx], esophagus [carcinoma - esophagus], cervix uterus [carcinoma - cervix], and thyroid gand [carcinoma - thyroid gland]. These tumors can spread to regional lymph nodes and to distant sites giving rise to metastases [carcinoma - metastatic]. In the ocular tissues a squamous cell carcinoma most often arises in the eyelid [carcinoma - eyelid] and conjunctiva [carcinoma - conjunctiva]. In the Western Hemisphere squamous cell carcinoma of the eyelid  [squamous carcinoma - eyelid] accounts for ~9% of all malignancies in the eyelid. A squamous cell carcinoma often grows in a papillary or exophytic manner. It is characterized histopathologically by cellular atypia and individual neoplastic cells or nests of tumor cells extend beyond the base of the affected epithelium into the underlying stroma. The epithelium is sometimes keratinized. The adjacent epithelium frequently has an intraepithelial neoplasm. The tumor cells possess immunohistochemically detectable intracytoplasmic cytokeratin and epithelial ultrastructural features such as desmosomes and tonofibrils.