Abstract:

Spiradenocarcinoma, (malignant eccrine spiradenoma), is an exceedingly rare adnexal carcinoma with unknown incidence. Precursor lesions such as spiradenoma, cylindroma, or spiradenocylindroma can undergo malignant transformation over a 6-month to 70-year period. We present a 41-year-old male, with a past medical history significant for untreated Hepatitis C, who presented with an increasingly symptomatic mass of the right thigh mass, present for over 10 years. The mass was tender to palpation, pruritic, and associated with paresthesias of the right lower extremity. Physical exam revealed a fixed nodule in the upper right thigh. Computed Topography (CT) imaging demonstrated a heterogeneously enhancing mass within the subcutaneous soft tissue. Histopathological examination revealed a multi-lobular, well circumscribed, dermal tumor comprised of basaloid cells. The tumor was composed of bland cells with a biphasic morphology with a focus of cells with increased mitotic activity which had lost the expected biphasic morphology. Immunohistochemical (IHC) stains demonstrated partial loss of staining for SMA, p63, S100, and CAM5.2 in areas of decreased differentiation. These IHCs were appropriately retained in areas with classic morphology. The histologic findings are compatible with a low-grade or in-situ spiradenocarcinoma. Distinguishing spiradenocarcinoma from spiradenoma can be challenging, particularly in low-grade cases. Histologic findings supporting malignancy include atypical mitotic figures, nuclear atypia, absence of biphasic cell population, and a clear transition in cell morphology. These lesions are traditionally regarded as high-grade malignant with poor overall prognosis, characterized by potential for metastatic disease and associated mortality. Due to this tumor’s metastatic potential, prompt diagnosis is critical to improving mortality.

Financial Disclosure:
No current or relevant financial relationships exist.

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Alyssa Higgins, DO