Treatment with metformin is associated with higher remission rate in diabetic patients with thyroid cancer

Context: Clinical trials demonstrated that metformin increases the efficiency of systemic therapy in cancer patients. Objective:Weexamined whether the efficacy of conventional treatment of differentiated thyroid cancer (DTC) is affected by therapy with metformin in diabetic patients. Design:Wecomparedthe rate of complete response (CR)betweendiabeticswhoweretreated with metformin (group MF+; n = 34) or not treated (group MF+; n = 21) and control nondiabetic patients (group C; n = 185). We also examined the effects of metformin on DTC cells in vitro. Results: The groups were comparable in terms of age, sex, body mass index, diabetes management, frequencies of multifocal tumor growth, extrathyroidal extension, and locoregional and distant metastases. Tumor size was significantly smaller in theMF+group compared with theMF+and C groups (1.37±0.97 vs 2.44±1.49 vs 2.39±1.73 cm, respectively; P=.026).Amultivariate model revealed that extrathyroidal extension (P = .018), distant metastases (P < .0001), and lack of treatment with metformin of diabetics (P<.0001) decreased the likelihood of CR. A Cox hazards model revealed that age (P=.025), locoregional metastases (P=.022), distant metastases (P=.003), and lack of treatment with metformin of patients with diabetes (P = .014) are associated with increased risk for shortened progression- free survival. In vitro data revealed that metformin inhibited cancer cell growth, activated cAMP-inducible protein kinase (5'-AMP-activated protein kinase [AMPK]), and down-regulated p70S6K/pS6. Metformin potentiated H ₂O₂-inducible activation of AMPK but attenuated pERK and p70S6K. Tumors from MF+ patients demonstrated a lower level of phospho-p70S6K compared with the MF+ group. Conclusions: Tumor size is smaller in patients treated with metformin, suggesting inhibition of tumor growth by the drug. Among diabetics, the absence of metformin therapy is an independent factor for decreased likelihood of CR and increased risk of shorter progression-free survival. In vitro data suggest that p70S6K/pS6 is likely a molecular target of metformin in DTC cells.