Abstract:

Digital papillary adenocarcinoma (DPA) is an uncommon adnexal tumor primarily of the digits with risk for local recurrence and distant metastasis. No known histologic features accurately predict clinical outcome. We report a case of DPA without papillary architecture, a potential diagnostic pitfall. A 41-year-old female presented with a longstanding palpable mass of her left index finger. There were no overlying skin changes. Microscopic examination shows a well-circumscribed nonencapsulated solid and cystic tumor composed of epithelioid cells with random nuclear pleomorphism and rare mitoses. Intralesional ducts, cartilaginous metaplasia and hyalinized basement membrane material are noted. No definitive papillary structures, atypical mitoses or tumor necrosis are seen. By immunohistochemistry, the tumor cells are diffusely positive for AE1/3 and CK5/6, show patchy staining with S100 and are negative for SMA. EMA stains luminal border of intralesional ducts. p63 and p40 expression is limited to scattered peripherally located tumor cells. This case illustrates the usefulness of immunohistochemistry differentiating DPA without papillary architecture from hidradenoma, a benign adnexal tumor initially considered (Am J Surg Path 2020:44:711-717). The patient underwent additional resection of the surgical site and had negative sentinel lymph node biopsies (0/3). The absence of papillary architecture in this case confounded the difficulty in differentiating DPA from hidradenoma. The combined morphology and immunoprofile lead to the correct diagnosis requiring further clinical intervention and long term clinical surveillance.

Financial Disclosure:
No current or relevant financial relationships exist.

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Anne Dharamraj, MD