Dual-Tracer PET/CT in Erysipelas-like Cutaneous Metastases From Salivary Duct Adenocarcinoma: FAPI Illuminates What FDG Missed.

Thakur, Sonali; Raju, Shobhana; Rajguru, Renu; Chowhan, Amit Kumar; Prabha, Neel; Ravina, Mudalsha · Clin Nucl Med · 2026

case_report · Level V

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Abstract

Cutaneous metastases are rare manifestations of malignancies. We report a case of a 50-year-old man with an atypical presentation of erysipelas-like skin lesions, later found to be cutaneous metastases from an unknown primary. 18 F-FDG PET/CT revealed visceral metastases; however, it failed to demonstrate uptake in the skin lesion, while 68 Ga-FAPI PET/CT additionally showed intense uptake in the skin, including the right parotid gland, which is likely the primary site. IHC findings confirmed a primary salivary duct adenocarcinoma. This case underscores FAPI PET/CT's utility in detecting FDG-negative lesions and identifying occult primaries in atypical presentations, also reflecting the intratumoral heterogeneity of salivary duct carcinomas.

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