Longitudinal changes in pancreatic neuroendocrine tumor (panNET) cell proliferation correlate with fast disease progression and poor prognosis. The optimal treatment strategy for secondary panNET grade (G)3 that has progressed from a previous low- or intermediate-grade to high-grade panNET G3 is currently unknown. This was a single-center retrospective cohort study aimed to characterize treatment patterns and outcomes among patients with secondary panNET-G3. Radiological responses were assessed using the Response Evaluation Criteria in Solid Tumors version 1.1. A total of 22 patients were included and received a median of 2 (range, 1–4) treatment lines in 14 different combinations. Median overall survival (OS) was 9 months (interquartile range (IQR): 4.25–17.5). For the 15 patients who received platinum–etoposide chemotherapy, median OS was 7.5 months (IQR: 3.75–10) and median progression-free survival (PFS) was 4 months (IQR: 2.5–5.5). The 15 patients who received conventional panNET therapies achieved a median OS of 8 months (IQR: 5–16.75) and median PFS was 5.5 months (IQR: 2.75–8.25). We observed one partial response on 177Lu DOTA-TATE therapy. In conclusion, this hypothesis-generating study failed to identify any promising treatment alternatives for patients with secondary panNET-G3. This demonstrates the need for both improved biological understanding of this particular NET entity and for designing prospective studies to further assess its treatment in larger patient cohorts.