Metformin Downregulates the STAT Pathway and Reduces Bone Marrow Fibrosis in Primary Myelofibrosis Patients: Final Results of the Phase II FIBROMET Trial

Primary myelofibrosis (PMF) is a chronic myeloproliferative neoplasm characterized by the activation of the JAK-STAT pathway. Previous evidence showed that metformin might be a possible therapeutic option for treating JAK2-mediated myeloproliferative neoplasms. In vitro and in vivo studies demonstrated that metformin inhibits the JAK-STAT pathway, induces apoptosis in JAK2^V617F-positive cell lines and reduces tumor burden and splenomegaly in Jak2^V617F knock-in-induced mice. The FIBROMET trial, an open label phase II study, evaluated metformin effects on 10 primary myelofibrosis patients over 2 years of treatment. Primary endpoint was bone marrow fibrosis reduction. Secondary endpoints were constitutional symptoms, blood counts, spleen size modulation and exploratory evaluation of protein and gene expression. Metformin treatment reduced bone marrow collagen deposits, downregulated the STAT pathway and reduced the p85 subunit of PI3K enzymatic complex, together with endothelial maintenance genes, in PMF patients. These results raise new evidence regarding metformin, a cheap and widely available drug, as a possible adjuvant for the treatment of PMF patients.