Printed in U.S.A. LETTERS TO THE EDITOR RE: “ENVIRONMENTAL TOBACCO SMOKE AND RISK OF MALIGNANT LYMPHOMA IN PET CATS”

The paper by Elizabeth Bertone et al. (1) on environmental tobacco smoke exposure and the increased risk of malignant lymphoma in pet cats is unconvincing. For the association of active smoking in humans and risk of non-Hodgkin’s lymphoma, most large studies have shown no increased risk. A recent review of all cohort and case-control studies concluded that there were no grounds for rejecting the null hypothesis (2). The relative risk of 3.8 quoted by Bertone et al. was for the smallest cohort study that represented a sample size of 2 percent of all cohort studies (3). A similar small study gave the opposite result with a relative risk of 0.58 (2). Coupled with this is the ines-capable observation that the incidence of non-Hodgkin’s lymphoma has increased year by year since 1975 despite increasing smoking cessation during the last four decade