Durable complete metabolic responses to androgen receptor-targeted therapy in metastatic primary cutaneous apocrine carcinoma: a case report and literature review.

BACKGROUND: Primary cutaneous apocrine carcinoma (PCAC) is an exceptionally rare adnexal malignancy with limited evidence to guide systemic treatment. Androgen receptor (AR) expression is common, but durable responses to AR-targeted therapy have been reported only in isolated cases. This case highlights a uniquely reproducible and profound complete metabolic response to AR blockade in metastatic PCAC, offering valuable insight into its potential hormonal dependence. CASE PRESENTATION: A 57-year-old man with AR-strong PCAC of the axilla developed metastatic relapse involving mediastinal and axillary lymph nodes, lung lymphangitic spread, and a lytic vertebral lesion. Treatment with enzalutamide combined with goserelin resulted in a rapid and complete metabolic response on PET-CT. After therapy interruption due to cumulative fatigue and vasomotor symptoms, mild nodal progression and a new cutaneous recurrence occurred. Re-induction with the same regimen again resulted in complete metabolic and radiologic remission, which remained durable on follow-up. CONCLUSION: This case demonstrates that AR-targeted therapy may induce deep, durable, and reproducible metabolic responses in AR-positive metastatic PCAC, even after treatment re-challenge. Comprehensive molecular and immunohistochemical profiling is essential for identifying actionable pathways in this rare tumour. The findings contribute meaningful evidence to the limited literature and may support further investigation of AR signalling as a therapeutic target in PCAC.