P019 Digital papillary adenocarcinoma: an important differential for digital tumours

Abstract Digital papillary adenocarcinomas are rare aggressive tumours with significant metastatic potential, arising from sweat glands (Weingertner N, Gressel A, Battistella M, Cribier B. Aggressive digital papillary adenocarcinoma: a clinicopathological study of 19 cases. J Am Acad Dermatol 2017; 77: 549–58). Diagnosis is challenging due to their rarity and histopathological features, showing similarities to benign sweat gland tumours. Furthermore, optimal management presents difficulties due to lack of standardized guidelines. We present the case of a 45-year-old man with a 4-year history of a slow-growing painless nodule on the left middle finger. Examination revealed a firm 1-cm purple–red subcutaneous swelling adjacent to the distal interphalangeal joint. Primary excision demonstrated intraoperative findings of a well-circumscribed lesion within the subcutaneous tissue anterior to the extensor tendon. Histopathological examination identified a multinodular basaloid proliferation of cells in variably solid, papillary and cystic architecture within subcutaneous tissue. Mild cellular pleomorphism was seen with prominent mitotic activity. Immunohistochemistry showed diffuse positivity for CK7, peripheral myoepithelial cell staining for p63, and central epithelial membrane antigen-positive luminal lining. Human papillomavirus 42 positivity was demonstrated on polymerase chain reaction testing, further establishing a histopathological diagnosis of digital papillary adenocarcinoma, confirmed with clinicopathological correlation. Histopathological clearance was achieved following amputation of the midproximal phalanx. Staging computed tomography (CT) imaging of head and neck, chest, abdomen and pelvis was negative for metastatic disease. Clinical and imaging surveillance is ongoing. This case highlights the clinical presentation and histopathological features of a rare adnexal tumour, digital papillary adenocarcinoma, which can mimic benign nodules such as ganglion cysts, and cystadenomas. Given its aggressive nature and metastatic potential, prompt consideration of the diagnosis by dermatologists is critical to ensure timely diagnosis and effective multidisciplinary team management.