Abstract

A subtype of eccrine carcinoma, squamoid eccrine ductal carcinoma is an exceedingly rare diagnosis that shows eccrine ductal differentiation with admixed atypical squamous proliferation with squamous eddies and keratin cysts. Usual clinical presentation includes nodules on the head and neck and extremities in elderly males. The rarity of this lesion lends itself to misdiagnosis on initial biopsy as nearly half of the cases end up being called squamous cell carcinoma. A high rate of local recurrences, lymphovascular invasion, perineural invasion, and metastases have been reported necessitating the need for a close clinical follow up. Here, we present the case of squamoid ductal eccrine carcinoma in a 64-year-old female patient who presented with a persistent lesion on the medial aspect of her heel. An initial excisional biopsy of the specimen showed morphologic properties of a low-grade ductal eccrine adenocarcinoma with squamous differentiation that exhibited immunoreactivity for P63. The biopsy specimen had positive margins. Two years later, the follow up excision biopsy of the recurred lesion at the same site showed invasive nests of mixed population of smaller basaloid adnexal cells and larger squamous cells with some surrounding ductal lumina, histomorphologically similar to the initial tumor. Additionally scattered infundibulocystic keratinizing structures were also present. In addition to P63, CK7 was positive in cells of interest. Taken together with the prior biopsy specimen, a diagnosis of squamoid ductal eccrine carcinoma was made. The unconventional site, in combination with the exceedingly rare nature of this diagnosis affords it a diagnostic import and interest.