Squamoid Eccrine Ductal Carcinoma: Case Series of a Rare, Potentially Aggressive Skin Cancer Associated With Immunosuppression

Squamoid Eccrine Ductal Carcinoma (SEDC) is a rare cutaneous adenexal carcinoma first described in 1997. It has distinct biphasic features on histology which commonly result in misdiagnosis as Bowen disease or cutaneous squamous cell carcinomas (cSCC) if diagnostic skin biopsies are too superficial. This may lead to a delay in diagnosis. It is locally aggressive with significant metastatic potential, and an association with immunosuppression has been previously reported in ~20% of cases. We conducted a single‐centre, retrospective cohort study of all patients diagnosed with SEDC over a 12‐year period (2013–2025). Ten cases were identified (7 M, 3 F; mean age at diagnosis 75 years [SD 10.8]), of whom 9 (90%) were immunocompromised due to solid organ transplantation ( n = 6) or haematologic malignancy ( n = 3). A diagnosis of SEDC was not initially made in any of the 4 cases in which an incisional biopsy was performed and only correctly diagnosed after complete excision. Locoregional recurrence occurred in 8 (80%) and distant metastasis in 2 (20%) of patients. Treatment included surgical excision in all cases, post‐operative radiotherapy due to incomplete or close margins or metastasis in 60%, and lymphadenectomy or parotidectomy in 20%. This case series highlights the diagnostic challenges posed by SEDC and the need for clinicopathologic vigilance, its potentially aggressive course, and the apparent strength of the association with immunosuppression which we propose may have been previously underestimated.