Digital papillary adenocarcinoma: A case report of a rare malignant tumour with recommendations on management and follow-up.

Introduction: Digital papillary adenocarcinoma (DPAC) is a rare malignant tumour of the sweat glands, usually in the digits. It has a high rate of recurrence and metastasis, yet there's a lack of guidelines for its diagnosis and management. Therefore, this report aims to evaluate procedures that provide the best outcomes, which will help create a consensus for its management.

Case Presentation: This case report presents a 47-year old male who had a painless hyperkeratotic patch on his left index finger, with an additional cystic lesion underlying it. This was diagnosed as a hidradenoma, which later changed to DPAC. His finger was amputated through the head of the middle phalanx. A positive sentinel lymph node biopsy led to a left axillary lymph node dissection, which revealed micrometastasis. The patient declined radiotherapy and was on a melanoma follow-up plan. To date there is no evidence of recurrence.

Clinical Discussion: Reviewing studies supported the use of immunohistochemical analysis to identify specific markers, especially HPV42. Sentinel lymph node biopsy and radical excision or amputation had the lowest rate of recurrence and thus should be common practice alongside long-term follow-up. Specific follow-up criteria are debated, yet this case may offer a solution by following the melanoma criteria.

Conclusion: Histological and immunohistochemical analysis (including HPV42 detection), SLNB, and radical excision or amputation are optimal for DPAC management. Long-term follow-up, possibly using melanoma criteria, is crucial. Further research is needed to establish definitive guidelines.