Nonconventional Doses of Somatostatin Analogs in Patients with Progressing Well-Differentiated Neuroendocrine Tumor

Purpose: To evaluate the antiproliferative activity and safety of nonconventional high doses of somatostatin analogs (HD-SSA) in patients with well-differentiated gastroenteropancreatic (GEP) neuroendocrine tumors (NET) with radiological disease progression according to Response Evaluation Criteria in Solid Tumors (RECIST) criteria on a previous treatment. Methods: A retrospective analysis of prospectively maintained databases from 13 Italian NET-dedicated centers was performed. Main inclusion criteria were: well-differentiated G1 or G2 GEP-NET, progressive disease on a previous treatment, and subsequent treatment with HD-SSA (either by increased administered dose [dose intensity] or shortened interval between administrations [dose density]). Main endpoints were progression-free survival (PFS) and safety. Results: Of 198 patients, 140 matched inclusion criteria and were included in the analysis. Overall, median PFS was 31 months. Use of HD-SSA as second-line treatment was associated with reduced risk for progression or death compared with third- or further-line treatment (HR: 2.12; P = 0.004). There was no difference in PFS between HD-SSA by increased dose density (N = 133; 95%) or intensity (N = 7; 5%). Partial response according to RECIST criteria was observed in 12 patients (8.6%), and stable disease was achieved in 106 (75.7%) patients. Adverse events occurred in 21 patients (15.0%), 2 of whom had grade 3 biliary stone disease. No patients discontinued HD-SSA treatment due to adverse events. Conclusions: HD-SSA is an active and safe treatment option in patients with progressive well-differentiated GEP-NET. The high rate of objective responses observed deserves prospective validation in ad hoc clinical trials.