Metformin May Not Improve Survival in Patients with Pancreatic Cancer

May 2015, Vol 6, No 4

Philadelphia, PA—Several retrospective studies have shown that metformin is associated with longer survival in patients with cancer, including pancreatic cancer. However, in a new study led by Roongruedee Chaiteerakij, MD, PhD, Division of Gastroenterology and Hepatology, Mayo Clinic Cancer Center, Rochester, MN, metformin did not improve survival for patients with pancreatic ductal adenocarcinoma (PDAC). The results were presented at the 2015 American Association for Cancer Research meeting.

Chaiteerakij and colleagues used data from the Mayo Clinic Specialized Programs of Research Excellence pancreatic cancer database. The study included 1360 patients (59% male; mean age, 67 years) with PDAC who have been taking metformin; overall survival was the primary outcome.

Patients were categorized into 5 groups based on the use of metformin:

  1. Never used (N = 908)
  2. Metformin started >1 year before PDAC diagnosis (N = 84)
  3. Metformin started within 1 year before PDAC diagnosis (N = 212)
  4. Metformin started <30 days after PDAC diagnosis (N = 104)
  5. Metformin started >30 days after PDAC diagnosis (N = 34).

“The diabetes drug metformin is being used in some cancer treatment trials based on epidemiologic studies that have reported that use of metformin reduces the risk of death from cancer,” Dr Chaiteerakij stated.

Because retrospective studies of cancer survival may have unintended biases related to the complexity of diabetes management, this study addressed these inherent biases.

“This study highlights the importance of appropriate design of retrospective studies and the necessity of conducting prospective studies with solid rationale for determining the effect of diabetes drugs on cancer risk or death,” Dr Chaiteerakij said.

The median survival of patients who used metformin was 292 days compared with 308 days for nonusers, a nonsignificant difference. However, among the 413 patients with resectable cancer, those who used metformin survived longer than nonusers—782 versus 612 days (P = .07).

This analysis suggests that metformin does not improve survival for most patients with PDAC, but those with resectable cancer who started metformin after PDAC diagnosis benefited from this medication. The researchers noted that there is an inherent survival bias in these patients.

“Studies of medication exposure and cancer survival warrant very careful and detailed data collection, which is not always possible in a retrospective study design,” Dr Chaiteerakij said. “Researchers should exercise caution when initiating clinical trials based on retrospective epidemiologic studies.”

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