Introduction
Tumor growth rate (TGR; percent size change per month [%/m]) is postulated to be an early radiological biomarker to overcome limitations of RECIST. This study aimed to assess the impact of TGR in neuroendocrine tumors (NETs) and potential clinical and therapeutic applications.
Materials and Methods
Patients (pts) with advanced grade (G) 1/2 NETs from the pancreas or small bowel initiating systemic treatment (ST) or watch and wait (WW) were eligible. Baseline and followâup scans were retrospectively reviewed to calculate TGR at pretreatment (TGR0), first followâup (TGRfirst), and 3(±1) months of study entry (TGR3m).
Results
Out of 905 pts screened, 222 were eligible. Best TGRfirst (222 pts) cutoff was 0.8 (area under the curve, 0.74). When applied to TGR3m (103 pts), pts with TGR3m <0.8 (66.9%) versus TGR3m â„ 0.8 (33.1%) had longer median progressionâfree survival (PFS; 26.3 m; 95% confidence interval [CI] 19.5â32.4 vs. 9.3 m; 95% CI, 6.1â22.9) and lower progression rate at 12 months (7.3% vs. 56.8%; p = .001). WW (vs. ST) and TGR3m â„ 0.8 (hazard ratio [HR], 3.75; 95% CI, 2.21â6.34; p < .001) were retained as factors associated with a shorter PFS in multivariable Cox regression. TGR3m (HR, 3.62; 95% CI, 1.97â6.64; p < .001) was also an independent factor related to shorter PFS when analysis was limited to pts with stable disease (81 pts). Out of the 60 pts with TGR0 data available, 60% of pts had TGR0 < 4%/month. TGR0 â„ 4 %/month (HR, 2.22; 95% CI, 1.15â4.31; p = .018) was also an independent factor related to shorter PFS.
Conclusion
TGR is an early radiological biomarker able to predict PFS and to identify patients with advanced NETs who may require closer radiological followâup.
Implications for Practice
Tumor growth rate at 3 months (TGR3m) is an early radiological biomarker able to predict progressionâfree survival and to identify patients with advanced neuroendocrine tumors who may require closer radiological followâup. It is feasible to calculate TGR3m in clinical practice and it could be a useful tool for guiding patient management. This biomarker could also be implemented in future clinical trials to assess response to therapy.