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Case Reports

Abstract

Digital papillary adenocarcinoma (DPA) is a rare neoplasm, with roughly 1 in 4 cases recurring and 1 in 5.5 cases metastasizing. In our case, a 31-year-old patient presented with a slowly growing mass over 10 years on the 4th toe following trauma. MRI revealed a capsuloligamentous mass measuring 1.9 x 1.3 x 0.8 cm and abutting the extensor tendon sheaths. The patient underwent an incisional biopsy. Histologically, the lesion was identified as a nodular dermal adnexal proliferation embedded in a fibrotic stroma and characterized by round and elongated tubular adnexal structures with apocrine and eccrine differentiation, as well as intraluminal papillary projections. The proliferation involved all margins, so the overall architecture was not discernible. Rare mitoses were noted, but the Ki-67 proliferative index was low. BRAF V600E immunostaining showed weak positivity throughout the neoplasm. While the differential diagnosis included an apocrine/eccrine adenoma, given the lesion’s size, its location, and the infiltrative features at the tumor periphery, digital papillary adenocarcinoma could not be excluded, and it was advised that it be treated as such. The patient was referred for digital amputation with sentinel lymph node biopsy. A chest X-ray was negative for metastasis. This case highlights the importance of differentiating DPA from its benign mimickers, particularly when encountering adnexal proliferation on distal extremities. Although non-specific, benign proliferation may harbor BRAF mutations. While the etiology of DPA is not entirely clear, an association with HPV-42 has been recently established. Treatment options range from excision to partial digit amputation with long-term follow-up.