VIENNA — The glucose-lowering drug metformin is increasingly showing an anticancer effect.
The data come from studies conducted in both the diabetes and oncology research communities, according to experts at the annual meeting of the European Association for the Study of Diabetes.
The subject first caught the medical community's attention this summer, with the publication of a series of articles on the putative association between insulin glargine and cancer in EASD's journal Diabetologia (I
The question has been whether glargine or other insulin analogues could accelerate the growth of cancers in patients predisposed to the disease. At the meeting, representatives from Sanofi-Aventis, maker of insulin glargine (Lantus), and Novo Nordisk, maker of detemir (Levemir), presented data showing no statistically significant relationship between their products and cancer.
But evidence for a protective effect of metformin did appear in one of the Diabetologia studies that caused the furor. Craig J. Currie, Ph.D., of Cardiff (Wales) University and his associates found the lowest risk for cancer among users of metformin, compared with other diabetes treatments; adding metformin to insulin reduced the progression to cancer, compared with insulin treatment alone, with a hazard ratio of 0.54 in a retrospective cohort study of more than 62,809 diabetes patients.
Several lines of investigation are now looking at metformin as a potential anticancer treatment outside of diabetes, said Dr. Edwin Gale, of the University of Bristol (England) and editor-in-chief of Diabetologia.
The Cardiff study showed that diabetes patients on insulin or insulin secretagogues were more likely to develop solid cancers than were those on metformin, while the combination with metformin abolished most of this excess risk. Metformin use was associated with lower risks of colon or pancreatic cancer, but did not affect the risk of breast or prostate cancer. Use of insulin analogues was not associated with increased cancer risk, compared with human insulin (Diabetologia 2009;52:1766–77).
Dr. Ulf Smith, president of the EASD, said that two just-published studies further support the notion that metformin may have a protective effect against cancer. One showed a better response rate to chemotherapy among diabetic patients with breast cancer who were taking metformin (J. Clin. Oncol. 2009;27:3297–302).
The other study, published online, supports the so-called “cancer stem cell” hypothesis, which suggests that, unlike most cancer cells within a tumor, cancer stem cells resist chemotherapeutic drugs and can regenerate the various cell types in the tumor, thereby causing relapse of the disease. Drugs that selectively target cancer stem cells offer promise for cancer treatment, particularly in combination with chemotherapy. In this study on mice, metformin inhibited cellular transformation and selectively killed cancer stem cells in four genetically different types of breast cancer, and the combination of metformin and doxorubicin killed both cancer stem cells and non-stem cancer cells in culture (Cancer Res. 2009 Sept. 14 [doi:10.1158/0008-5472.CAN-09-2994]).
“The story with metformin is extremely exciting,” said Dr. Smith of the Sahlgrenska Center for Cardiovascular and Metabolic Research, Göteborg, Sweden.
The lowest cancer risk was in patients who used metformin, compared with other diabetes treatments.
Source Dr. Currie