To the Editor.
—The data from the cohort study by Dr Chiu and colleagues1 relating diet to non-Hodgkin (NHL) lymphoma are intriguing. Evidence from prospective cohort studies is held to be more reliable in generating evidence supporting causal relationships than evidence from the other common design used in cancer epidemiology, the case-control study, in part because the temporal association between the exposure (in this case, dietary intake of red meat) and the disease (lymphoma) seems clear. That a putative cause should precede the disease is the sine qua non of any causal relationship. In spite of the design employed by Chiu et al,1 however, the temporal relationship between diet and cancer might not be as clear as it seems; cancers do not arise spontaneously, but grow until symptoms lead the affected individual to seek medical attention. Some proportion of the women diagnosed with cancer in the study by
Kritchevsky SB. Meat Intake and Non-Hodgkin Lymphoma. JAMA. 1996;276(7):524. doi:10.1001/jama.1996.03540070020011