To explore potential synergy in effectiveness between metformin and everolimus, 2 inhibitors of the mTOR pathway, for neuroendocrine tumours (NET).

A cohort of patients with advanced gastroenteropancreatic or lung NETs treated by everolimus were stratified in to those without diabetes, those with diabetes and without metformin, and those with diabetes with metformin. The primary endpoint was the median progression-free survival (PFS).

A total of 213 patients were included, 165 of which were non-diabetic; among diabetic patients, 19 were treated with metformin and 29 with others anti-diabetic drugs. No significant difference in median PFS [95%CI] was found between the three groups: 10.05 months [8.27;11.83] for non-diabetic patients, 15.24 [19.88;49.43] for diabetic w/metformin, and 9.03 months [4.01;14.06] for diabetic w/o metformin group. In univariate analysis, factors significantly associated with longer PFS was a functioning NET, a number of metastatic sites<3, the absence of lung metastasis, and an uptake on Octreoscan®, but not the absence of metformin use; only uptake on Octreoscan® remained significant in multivariate analysis.

In contrast with the literature, we did not find a synergy between everolimus and metformin in NET. Prospective studies are underway to improve the comprehension of the potential synergy regarding population and tumour type.