Findings of a retrospective analysis suggest that patients with well-differentiated metastatic/unresectable grade 3 gastroenteropancreatic neuroendocrine tumors (GEP-NETs) may derive modest progression-free survival (PFS) benefit with somatostatin analog (SSA) monotherapy.
Although the efficacy of SSA monotherapy has been demonstrated for lower-grade (1/2) NETs, its role in well-differentiated grade 3 NETs is undefined. A retrospective analysis was performed to evaluate the efficacy of SSAs in metastatic/unresectable grade 3 GEP-NETs; the results of this analysis were reported at the 2020 North American Neuroendocrine Tumor Society Annual Symposium.
This retrospective chart review included eligible patients in the Mayo Clinic from 1992 to the present. Eligibility criteria included patients with centrally reviewed, pathology-confirmed, metastatic/unresectable, well-differentiated grade 3 NETs, who had received SSA monotherapy and for whom radiologic data were available to assess the response. Patients who had received prior lines of treatment were included as long as they were subsequently treated with SSA monotherapy. The primary end point was PFS; the secondary end point was assessment of best overall response. Rb1 and p53 status was also assessed by immunohistochemistry in well-differentiated versus poorly differentiated NETs.
Of the 90 patient records reviewed, 16 met eligibility criteria and were included in the analysis. The median age was 58 years, and 56% were female, with primary tumor sites in the pancreas (N = 7), small bowel (N = 5), stomach (N = 3), and duodenum (N = 1); the majority of patients had metastasis to the liver (N = 14) and lymph node (N = 6). The median Ki67 proliferative index was 26%.
Overall, 2 patients achieved a partial response (PR), and 7 patients had stable disease (SD). The estimated median PFS was 4.4 months (95% confidence interval [CI], 3.1-24). Of the 9 patients with SD or PR, the median time to progression was 16.3 months (95% CI, 4.4-45). Overall survival was not estimable. Ki67 index did not correlate with PFS based on a proportional hazards model. In evaluable tumors, p53 and Rb1 showed wild-type phenotype, which was consistent with a well-differentiated genomic signature.
The results of this retrospective analysis suggest SSA use had a modest PFS benefit in well-differentiated metastatic/unresectable grade 3 GEP-NETs.
Source: McGarrah P, et al. North American Neuroendocrine Tumor Society 2020 Annual Symposium; October 1-3, 2020. Abstract C20.
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