There is increasing evidence from epidemiological studies and scientific research that metformin may have an antitumor effect. However, whether the drug improves survival in cancer patients with diabetes remains unclear to date, as the study situation is contradictory.
In a meta-analysis, two Chinese researchers compiled data from various epidemiological studies to determine the extent to which metformin can actually prolong survival in cancer patients with diabetes or is associated with longer survival [1].
A total of 28 studies were examined. It was shown that the risk scores regarding all-cause mortality under metformin were significantly lower than the risk rates in patients not receiving metformin, especially for breast cancer, colorectal cancer, ovarian cancer, and endometrial cancer. Cancer-specific mortality was also lower with the substance.
The last word is not yet spoken
In the past, there have been repeated studies showing a survival benefit of cancer patients with diabetes (given the plausible antitumor mode of action of metformin, this is understandable), but the overall study situation remained contradictory.
This meta-analysis strengthens the hypothesis that such a beneficial effect of metformin may indeed exist. The lower mortality was reflected in the following values:
- Breast cancer (“pooled relative risk” [RR] 0.70, 95% CI 0.55, 0.88; p=0.003)
- Colorectal cancer (RR 0.70, 95% CI 0.59, 0.84; p<0.001).
- Ovarian cancer (RR 0.44, 95% CI 0.30, 0.64; p<0.001).
- Endometrial cancer (RR 0.49, 95% CI 0.32, 0.73; p=0.001).
Consequently, the risk of death was reduced by 30 for breast and colorectal cancer, 51 for endometrial cancer and 56% for ovarian cancer. The results must be put into perspective in that the studies were very heterogeneous and in some cases contained too little information on the cancer therapy used and the metformin dosage.
Outlook
Prognostic factors such as tumor size, type, stage, and existing metastases were not considered in the studies. Therefore, there is a need to catch up here for future research. Only in this way will it be possible to better understand in detail the relationship between taking metformin and better cancer survival.
Source: Zhang ZJ, Li S: The prognostic value of metformin for cancer patients with concurrent diabetes: a systematic review and meta-analysis. Diabetes, Obesity and Metabolism 2014; 16(8): 707-710.
