Coffee, pancreatic cancer and the question of causation

The article by Miquel Porta and his colleagues 1 indicating that pancreatic cancer cases without activating mutations in the K-ras gene drank significantly less coffee than cases with a mutation and the accompanying editorial by Paolo Vineis 2 are both important. The study by Porta and his colleagues has a considerable advantage over conventional case-control studies-it is less likely to have suffered from substantial selection or information bias. 3 Unless chance has operated in a sinister way, you have to accept that there is indeed a positive association between coffee intake and K-ras mutations among patients with pancreatic cancer.