Abstract
The purpose of this study was to evaluate longitudinal changes in Ki-67 indices of SI-NETs and assess the impact of these in overall survival (OS). We screened 551 patients with SI-NETs diagnosed from 1993, through 2021, identified using the SI-NET databases from five European referral centres. Only patients with well-differentiated tumours and available baseline tumour samples, and follow-up re-biopsies were included. For tumour grading, apart from 2017 WHO classification system, we applied a recently proposed SI-NET site-specific modified histopathological grading system with Ki-67 cut-offs of 5 and 10%. We included 45 patients. Median Ki-67 index at SI-NET diagnosis was 2% (range 0.5-15%). Thirty-three patients had Ki67 indices <5% (70.2%), 6 had Ki67: 5-10% (12.8%) and 8 had Ki67 ≥10% (17%). Mean time to re-biopsy was 48.8 months (SD: +/-162.5). At re-biopsy, the median change in Ki-67 index (absolute value; follow-up minus time of diagnosis) was 1% (range -10 to +38%). An increase in Ki-67 occurred in 20 patients (42.6%); in 14 patients the change in Ki-67 resulted in progression to higher tumour grade following the modified grading system. Patients with an increment in Ki-67≥1% had a median OS of 32.9 months vs. 80.5 months in patients without (HR 5.6, 95% CI: 1.42-22.02, p=0.014). When applying the novel modified histopathological grading system for SI-NETs, patients with grade progression had a median OS of 32.9 months vs. 53.7 months in those without (HR=4.61, 95%CI: 1.22-13.54; p=0.022). At multivariable analysis, grade progression was confirmed as an independent predictor for death (HR=7.2, 95%CI: 1.58-32.82; p=0.011). Metachronous increment in Ki-67 indices and related grade progression over time following a site-specific modified histopathological grading system with Ki-67 cut-offs of 5 and 10% is observed in approximately 1/3 of SI-NETs included in this study and it is associated with worse survival outcomes.
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