Clinicopathologic Features and Treatment Outcomes of Squamoid Eccrine Ductal Carcinoma: A Comprehensive Retrospective Series.

Squamoid eccrine ductal carcinoma (SEDC) is an exceptionally rare malignant adnexal tumor that remains frequently underrecognized due to its overlapping clinical and histopathologic features with more common cutaneous neoplasms. This study presents a monocentric retrospective analysis of 16 patients with histologically confirmed SEDC diagnosed over a ten-year period. Clinical data, histopathologic parameters, immunohistochemical profiles, treatment approaches, and outcomes were systematically reviewed. The cohort predominantly comprised elderly individuals, with a male predominance and lesions arising mainly on sun-exposed areas of the head and neck. Clinically, SEDC manifested as erythematous or hyperkeratotic plaques or nodules often leading to an initial impression of squamous cell carcinoma. Histologically, tumors displayed the characteristic biphasic architecture with superficial squamoid differentiation and deeper ductal structures, frequently accompanied by subcutaneous infiltration or perineural involvement. Treatment consisted primarily of conventional excision, with complete margin clearance achieved in most cases; however, local recurrence occurred in 25% of patients, often within the first year. One patient developed distant metastases and died of disease. Clinical morphology, particularly erythematous plaque presentation, showed significant association with mortality, whereas deeper invasion demonstrated a trend toward worse outcomes. Despite its low metastatic potential, SEDC exhibits locally aggressive behavior, and diagnostic challenges remain common, especially on superficial biopsies. This series represents one of the largest single-center cohorts reported to date and underscores the importance of deep sampling, accurate histopathologic evaluation, and close clinical follow-up to optimize management of this rare adnexal carcinoma.