Wednesday, June 5, 2013

Pancreatic Cancer, Pancreatitis, and Diabetes.

     There was an article last week (Friday, May 31) on the front page of the business section of the NY Times quoting an interview with a doctor who claims that he has evidence that a diabetes drug, Januvia, can predispose the users to pancreatic cancer, based on animal studies.

     First, let me say a few words about all drug/animal studies. Animals have very different biochemical milieus than do humans, and the results of animal studies may not apply to humans. As an example of the difference, every animal but man and the guinea pig have the necessary enzymes to synthesize ascorbic acid, or Vitamin C. So already their chemistry is different. It is not automatic that a drug that has effect A on animals will have effect A on humans, and vice versa.

     Several decades ago, Congress passed a law with the Delaney clause, saying that any food additive that caused tumors in animals could not be added to food for humans. Shortly thereafter it was found that saccharine caused tumors in mouse bladders. Since saccharine was the only synthetic sweetener then available, Congress immediately passed a law exempting saccharine. So even the lawmakers don't believe the animal-human link.

     The changes that Dr. Peter Butler found were "pre-cancerous" lesions in rats, and no one knows how many precancerous lesions progress or what the time frame is. Post-marketing surveys have found no increased incidence of pancreatic cancers in users of Januvia, but there is argument as to whether or not there is an increased incidence of pancreatitis. As I have said before, if you have to argue about the significance of data, it almost certainly is not significant.

     What are the risk factors for pancreatic cancer? Age, obesity, chronic pancreatitis, and diabetes. The link with diabetes is tricky, because often pancreatic cancer first makes its presence known by causing diabetes. No one has shown that alcohol consumption is a risk factor for pancreatic cancer, even though it is a risk factor for chronic pancreatitis, and chronic pancreatitis is "linked" to pancreatic cancer, but not shown to cause it if you parse the observational data. OTOH extrapolating from diet studies, the Mediterranean diet should be protective.

     In summary, since diabetes itself is a risk factor for pancreatic cancer, the proper study would be to compare two groups of diabetics, one of whom takes Januvia while the other does not. And these patients should have the same diet vis-a-vis red meat and vegetables. I wonder if chronic pancreatitis is a risk factor for pancreatic cancer in lab rats? If it is not, then such a result would invalidate the  extrapolation from lab rats to humans.

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