A case of alopecic primary cutaneous adenoid cystic carcinoma successfully managed with the aid of prostate-specific membrane antigen-positron emission tomography imaging

Abstract

Primary cutaneous adenoid cystic carcinoma (PCACC) is a rare adnexal malignancy, most commonly affecting the scalp, and typically characterised by slow growth, marked local invasiveness and a high rate of local recurrence. Distant metastasis however remains uncommon. We report a case of a 58-year-old woman with a 6-year history of a progressively enlarging tender alopecic scalp lesion. Histopathology demonstrated a dermal basaloid neoplasm with tubular, nested and cribriform architecture and prominent perineural invasion, consistent with adenoid cystic carcinoma. Immunohistochemical studies highlighted a ductal cell component positive for cytokeratin 7 and CD117, and a myoepithelial cell component positive for smooth muscle actin and p40. Initial staging with ¹⁸F-fluorodeoxyglucose-positron emission tomography/ computed tomography (¹⁸F-FDG PET/CT) showed no significant metabolic activity or metastatic disease. Given emerging evidence of prostate-specific membrane antigen (PSMA) expression in adenoid cystic carcinoma, ⁶⁸Ga-PSMA PET/CT was performed and demonstrated moderate uptake confined to the primary scalp lesion without regional or distant disease. The patient underwent staged wide local excision with clear histological margins and split-thickness skin graft reconstruction.  Six-month follow-up ⁶⁸Ga-PSMA PET/CT showed no evidence of residual or recurrent disease. To the authors’ knowledge this is first documented case of PSMA-avid PCACC and suggests that ⁶⁸Ga-PSMA PET/CT may have a role in staging and surveillance of this rare tumour. Further studies are required to support these findings.