Abstract
Although basal cell carcinoma, squamous cell carcinoma, and melanoma represent the most frequent malignant tumors of the eyelids, a diverse group of rarer adnexal and neuroendocrine neoplasms also demonstrates a strong predilection for this anatomic site. These tumors, including sebaceous carcinoma, Merkel cell carcinoma, primary cutaneous mucinous carcinoma, endocrine-mucin-producing eccrine gland carcinoma (EMPSGC), primary apocrine adenocarcinoma, and primary signet ring (histiocytoid) carcinoma, are characterized by unique epidemiologic patterns, biologic behavior, and histopathologic features. The specialized microanatomy of the eyelid-with a dense concentration of meibomian (sebaceous), apocrine (Moll), and eccrine glands-combined with thin tissue planes, rich lymphovascular networks, and chronic ultraviolet exposure, contributes to their development, patterns of local invasion, and potential for metastasis. Accurate diagnosis often requires careful clinicopathologic correlation, incorporating immunohistochemical and molecular studies to distinguish primary lesions from eyelid metastases and identify syndromic associations. This review provides a comprehensive synthesis of the epidemiology, pathogenesis, clinical presentation, detailed histopathology, genetic alterations, differential diagnosis, management, and prognosis of these rare malignant eyelid tumors, with emphasis on early recognition and multidisciplinary care.