according to results of a retrospective study of patients with type 2 diabetes and stage IV cancer.
The analysis included 7,725 patients with lung, breast, colorectal, prostate, or pancreatic cancer identified through a search of a Surveillance, Epidemiology, and End Results (SEER)-Medicare dataset from 2007 to 2016.
Out of the full dataset, 2,981 patients (38.5%) had been prescribed metformin, and use was highest among patients with prostate cancer (46%).
Patients who took metformin versus those who did not had significantly better overall survival in both unadjusted (unadjusted hazard ratio [HR], 0.73; 95% confidence interval [CI], 0.69-0.76; P < .001) and adjusted models (adjusted HR, 0.77; 95% CI, 0.73-0.81; P < .001).
Lead author Lisa Scarton, PhD, RN, assistant professor, University of Florida College of Nursing, Gainesville, said that the “underlying mechanisms of metformin related to cancer are still not completely understood,” but many studies have shown metformin is associated with a reduction in the incidence of cancer, a reduction in cancer mortality, and an improvement in overall survival.
“As more evidence of anticancer benefit of metformin is emerging, it is important to explore optimal dosages that significantly improve cancer outcomes to boost anticancer effect,” she said in an interview.
Dr. Scarton presented the new data in a poster at the annual meeting of the American Association for Cancer Research.
The analysis found no significant difference in overall survival between patients who took metformin with average daily doses ≥ 1,000 mg or < 1,000 mg (aHR, 1.00; 95% CI, 0.93-1.08; P = .90).
Although the improvement in overall survival was seen in cancer subgroups, regardless of dose, Dr. Scarton noted the benefit was greatest among patients with breast cancer (aHR, 0.67; 95% CI, 0.56-0.82; P < .001). Hazard ratios among those who received metformin were 0.78 (95% CI, 0.69-0.88; P < .001) for colorectal cancer, 0.77 (95% CI, 0.72-0.82; P < .001) for lung cancer, 0.82 (95% CI, 0.72-0.93; P < .001) for pancreatic cancer, and 0.74 (95% CI, 0.62-0.88; P = .002) for prostate cancer. Also, she noted that race/ethnicity did not play a role as a significant factor for predicting better overall survival.
Among study limitations, Dr. Scarton said, was the advanced age of patients. “Our study population was 66 and older. It would be interesting to investigate this relationship among younger adults. We would also explore explicit benefits of metformin use in different racial and ethnic groups.”
The study was funded by the University of Florida. Dr. Scarton has reported no relevant financial relationships.
A version of this article first appeared on Medscape.com.