Tumor Growth Rate in Neuroendocrine Neoplasms: An Additional Tool for Treatment Strategies?

Background and Objectives: Neuroendocrine neoplasms (NENs) are rare, mainly gastro-entero-pancreatic tumors with heterogeneous biology and multiple therapeutic options. Assessing treatment response remains challenging. Standard evaluation relies on RECIST 1.1, although its limitations are well recognized. Tumor growth rate (TGR), defined as the monthly percentage change in tumor size between two imaging assessments, has been proposed as a dynamic parameter to complement conventional criteria. This review explores the role of TGR in NEN. Results: Two different evaluations of TGR, once conducted between baseline diagnostic scan and a radiological assessment 12-24 weeks after (TGR0), and another conducted between baseline scan and a diagnostic evaluation three months after (TGR3m), proved to be well correlated to progression free survival (PFS) in G1 and low-G2 NEN, with cut off of 4%/month and 0.8%/month, respectively. Conclusions: TGR offers additional insights into tumor kinetics and may help refine treatment monitoring in NEN. While retrospective evidence supports its prognostic utility, prospective studies are required to validate TGR as a standard clinical tool.