Somatostatin Receptor Expression on [⁶⁸Ga]Ga-DOTATATE PET Among Patients with Poorly Differentiated Extrapulmonary...

Limited data are available regarding somatostatin receptor (SSTR) expression in poorly differentiated extrapulmonary neuroendocrine carcinoma (NEC). Some retrospective series have reported strong SSTR expression in up to 40% of patients with NEC. However, these figures may be influenced by selection bias, such as imaging of patients with lower Ki-67 index or uncertainty about pathologic tumor differentiation. Methods: In this prospective study, [⁶⁸Ga]Ga-DOTATATE PET was compared with [¹⁸F]FDG PET in patients with metastatic extrapulmonary NEC and at least 1 measurable site of metastasis. The primary endpoint was the proportion of patients with tumors showing uniform [⁶⁸Ga]Ga-DOTATATE avidity (uptake greater than that in the normal liver). The secondary endpoint was the proportion of patients with no SSTR expression or a heterogeneous pattern of expression. Results: This study enrolled 30 patients who underwent [⁶⁸Ga]Ga-DOTATATE PET, 28 of whom also underwent [¹⁸F]FDG PET within a prespecified 2-mo interval from [⁶⁸Ga]Ga-DOTATATE PET. Primary tumor sites included the pancreas (n = 7), colon/rectum (n = 6), and uterus (n = 2); the sites of 9 primary tumors were unknown. Histologic subtypes included small cell (n = 15), large cell (n = 6), and mixed or unspecified types (n = 9). All patients had radiographically measurable metastases on cross-sectional imaging, although metabolic uptake on [¹⁸F]FDG PET may have been attenuated by prior chemotherapy administration in some cases. Only 4 patients (13%) had evidence of uniformly avid uptake (Krenning grade 3 or 4) on [⁶⁸Ga]Ga-DOTATATE PET, indicating strong SSTR expression. Conclusion: Avid, uniform SSTR expression was relatively uncommon in unselected patients with extrapulmonary NEC.