Cutaneous digital papillary adenocarcinoma: a clinicopathologic study of 31 cases of a rare neoplasm with new observations.

Aggressive digital papillary adenocarcinoma is a rare tumor predominantly involving the distal end of digits. We examined 31 cases of this distinctive tumor for clinicopathologic, immunohistochemical, and follow-up data where available. Males were predominantly affected (n=29), with a mean age of 43 years (range, 14 to 67 y). Three lesions were reported in patients below the age of 20 years. All cases involved a finger (n=26) or a toe (n=5), with most involving the distal portion of the digit (n=29). Two lesions involved the base of the digit/webspace. Histopathologically, all tumors involved the dermis with subcutaneous extension in 14 cases. The lesions demonstrated a multinodular solid and/or cystic pattern, with focally infiltrative architecture in 21 cases. Papillary projections were: prominent (n=10), focal (n=15), or not identified (n=6). Within the solid component, tubular structures were present at least focally in all cases. Cytologic atypia ranged from mild (n=8) to moderate (n=20), but was focally severe in 3 cases. Mitotic count ranged from <1 to 18 per mm. Focal necrosis was seen in 6 cases. Immunohistochemically stained sections were available for review in 8 cases. Tumor cells were diffusely positive for MNF116 (3 of 3). Carcinoembryonic antigen and epithelial membrane antigen highlighted the luminal border of tubules (8 of 8). Smooth muscle actin (5 of 6) and calponin (6 of 6) highlighted a myoepithelial layer around tubular/glandular structures, as did p63 (2 of 2) and podoplanin (5 of 5). Follow-up after excision or amputation (n=23; range, 2 mo- to 21 y) revealed local recurrence (n=5) and metastatic disease (n=6; lymph node in 1, lungs in 4, and both lymph node and lung in 1). Metastases were noted at presentation in 2 cases (lymph node in 1 and lung in 1), but presented as late as 14 and 20 years in lymph node and lung, respectively. Only 1 patient died of metastatic disease 6 years after initial diagnosis, after multiple recurrences and lung metastases. Three patients were alive with progressive disease up to 24 months after developing lung metastases. Histopathologic features were not found to be predictive of outcome. The presence of tumor-associated myoepithelial cells histologically and immunohistochemically was not synonymous with benignity. Wide excision and partial digit amputation significantly reduced recurrence and metastatic rates. Delayed occurrence of metastases and a protracted course despite metastatic disease, necessitates long-term follow-up. As the name implies a malignant neoplasm, the rubric "aggressive" is unnecessary.