The effect of metformin on the survival of colorectal cancer patients with type 2 diabetes mellitus

Evidence from previous studies suggests a protective effect of metformin in patients with colorectal cancer (CRC). The aim of this study was to examine the associations between metformin use and overall survival (OS) and disease-free survival (DFS) in CRC patients with type 2 diabetes mellitus (DM). We retrospectively included patients who underwent surgery for CRC at Limoges’ University Hospital between 2005 and 2019 and diagnosed with type 2 DM. Data on the characteristics of patients, CRC, comorbidities and drug exposure were collected from the electronic medical records. The exposure was the use of metformin and the outcomes were OS and DFS. We identified 290 CRC patients with type 2 DM. A total of 144 (49.7%) of them were treated with metformin. Metformin users were significantly younger, with higher body mass index and less diabetes-related complications compared to non-users. The 2-year OS was significantly higher in metformin users than in non-users (86.9 ± 2.9% vs. 71.0 ± 4.0%, p = 0.001). In multivariate analysis, metformin use was associated with better OS (adjusted hazard ratios [aHR] = 0.45 95% confidence interval [95% CI]: 0.21–0.96) and better DFS (aHR = 0.31; 95% CI: 0.18–0.54). In conclusion, the use of metformin may improve OS and DFS in CRC patients with type 2 DM.

Metformin kills and radiosensitizes cancer cells and preferentially kills cancer stem cells

The anti-cancer effects of metformin, the most widely used drug for type 2 diabetes, alone or in combination with ionizing radiation were studied with MCF-7 human breast cancer cells and FSaII mouse fibrosarcoma cells. Clinically achievable concentrations of metformin caused significant clonogenic death in cancer cells. Importantly, metformin was preferentially cytotoxic to cancer stem cells relative to non-cancer stem cells. Metformin increased the radiosensitivity of cancer cells in vitro, and significantly enhanced the radiation-induced growth delay of FSaII tumors (s.c.) in the legs of C3H mice. Both metformin and ionizing radiation activated AMPK leading to inactivation of mTOR and suppression of its downstream effectors such as S6K1 and 4EBP1, a crucial signaling pathway for proliferation and survival of cancer cells, in vitro as well as in the in vivo tumors. Conclusion: Metformin kills and radiosensitizes cancer cells and eradicates radioresistant cancer stem cells by activating AMPK and suppressing mTOR.

Survival advantage observed with the use of metformin in patients with type II diabetes and colorectal cancer

BACKGROUND

Patients with type II diabetes mellitus (DM) have an increased risk of adenomatous colorectal (CRC) polyps and CRC cancer. The use of the anti-hyperglycemic agent metformin is associated with a reduced incidence of cancer-related deaths.

METHODS

We retrospectively evaluated the medical records of 4758 patients seen at a single institution and determined that 424 patients were identified by their physicians as having type II DM and CRC cancer. Data were subsequently acquired determining the subject's age, body mass index (BMI), and disease date of diagnosis, stage, site of cancer, treatment, and survival.

RESULTS

Patients with type II DM and CRC cancer treated with metformin as one of their diabetic medications had a survival of 76.9 months (95% CI=61.4-102.4) as compared with 56.9 months in those patients not treated with metformin (95% CI=44.8-68.8), P=0.048. By using a multivariable Cox regression model adjusted for age, sex, race, BMI, and initial stage of disease, we demonstrated that type II diabetic patients treated with metformin had a 30% improvement in overall survival (OS) when compared with diabetic patients treated with other diabetic agents.

CONCLUSION

Colorectal cancer patients with DM treated with metformin as part of their diabetic therapy appear to have a superior OS.