Poorly Differentiated Neuroendocrine Carcinoma of the Parotid Gland and Moderately Differentiated Hepatic Metastases: A Discordant Histopathology Clarified by Dual-Tracer PET/CT.

This teaching case study illustrates a metastatic neuroendocrine neoplasm (NEN) of the parotid gland in which the histopathologic findings were discordant between the primary parotid tumor (poorly differentiated small cell neuroendocrine carcinoma) and a large hepatic metastasis (atypical carcinoid with moderately differentiation status; Ki-67, 15%-20%). The case study also illustrates the value of dual-tracer PET/CT imaging (68Ga-DOTATATE and 18F-FDG) in such a clinical setting. Minimal uptake of 68Ga-DOTATATE and high-grade uptake of 18F-FDG in the lesions indicated a poor differentiation status and helped to clarify the tumor biology, with potential implications for subsequent treatment-decision individualization in favor of chemotherapy. The findings underscore the clinical utility of dual-tracer PET/CT in making the appropriate assessment in patients with conflicting or discordant histopathologic findings at 2 sites.