PRRT in high-grade digestive neuroendocrine neoplasms (NET G3 and NEC)

Peptide receptor radionuclide therapy (PRRT) has been primarily studied in low and intermediate-grade digestive neuroendocrine tumors (NET G1-G2). The documentation of a similar benefit for high-grade digestive neuroendocrine neoplasms (NEN) has been limited. This review evaluates the use of PRRT for high-grade digestive NEN (well-differentiated NET G3 and poorly differentiated neuroendocrine carcinomas [NEC]). We identified one phase III trial and seven retrospective studies reporting specifically on PRRT outcome of >10 digestive high-grade NEN patients. The retrospective single-arm studies indicate a benefit for PRRT in NET G3. The randomized phase III NETTER-2 trial demonstrates major PFS superiority of PRRT versus somatostatin analog therapy as the first-line treatment for the NET G3 subgroup. PRRT can now be considered a potential first-line treatment for somatostatin receptor-positive NET G3 patients, but whether it should be the first-line standard of care for all NET G3 patients is still not clarified. For NEC, scarce data are available, and pathologic distinction between NEC and NET G3 can be difficult when Ki-67 is below 55%. PRRT could be considered as a treatment for refractory NEC in very selected cases when there is a high uptake on somatostatin receptor imaging, Ki-67 is below 55%, and there is no rapid tumor progression.