Metformin therapy reduces the risk of malignancy after heart transplantation.

BACKGROUND: Malignancy and diabetes mellitus (DM) cause significant morbidity and mortality after heart transplantation (HTx). Metformin, one of the most commonly used anti-diabetic drugs worldwide, has also been shown to exhibit anti-tumor activity. We therefore investigated the association between metformin therapy and malignancy after HTx.

METHODS: The study population comprised 237 patients who underwent HTx between 1991 and 2016 and were prospectively followed-up. Clinical data were recorded on prospectively designed forms. The primary outcome was any cancer recorded during 15 years of follow-up. Treatment with metformin and the development of DM after HTx were assessed as time-dependent factors in the analyses.

RESULTS: Of the 237 study patients, 85 (36%) had diabetes. Of the DM patients, 48 (56%) were treated with metformin. Kaplan-Meier survival analysis showed that, at 15 years after HTx, malignancy rate was 4% for DM patients treated with metformin, 62% for those who did not receive metformin and 27% for non-DM patients (log-rank test, p < 0.0001). Consistently, multivariate analysis showed that for DM patients, metformin therapy was independently associated with a significant 90% reduction (hazard ratio = 0.10; 95% confidence interval 0.02 to 0.40; p = 0.001) in the risk of the development of a malignancy. DM patients who were treated with metformin had a markedly lower risk (65%; p = 0.001) for the development of a malignancy or death after HTx as compared with non-DM patients.

CONCLUSIONS: Our findings suggest that metformin therapy is independently associated with a significant reduction in the risk of malignancy after HTx.