"Does Passive Smoking Cause Cancer in Pets?" TUMOR TIDBITS, A BIWEEKLY EMAIL NEWSLETTER FROM GULF COAST VETERINARY ONCOLOGY Number 68; September 6, 2002. ======================================================================= THIS WEEK'S TUMOR TIDBIT: DOES PASSIVE SMOKING CAUSE CANCER IN PETS? ======================================================================= There has been a number of news articles of late about second hand smoking and cancer occurring in cats and dogs. This Tidbit summarizes the two studies suggesting a link between passive smoke and lymphoma in cats and lung cancer in dogs. Drs. Bertone, Snyder and Moore (Department of Biostatistics and Epidemiology, School of Public Health and Health Sciences, University of Massachusetts, Amherst, MA) recently published in the American Journal of Epidemiology (2002, Volume 156(3):268-73) a retrospective study about the risk(s) of malignant lymphoma in pet cats in households with second-hand smoke exposure. Several human studies have suggested that smoking may increase the risk of non-Hodgkin's lymphoma. To evaluate whether exposure to household environmental tobacco smoke (ETS) may increase the risk of feline malignant lymphoma, the authors conducted a case-control study of this relation in 80 cats with malignant lymphoma and 114 controls with renal disease diagnosed at a large Massachusetts veterinary teaching hospital between 1993 and 2000. Owners of all subjects were sent a questionnaire inquiring about the level of smoking in the household 2 years prior to diagnosis. After adjustment for age and other factors, the relative risk of malignant lymphoma for cats with any household ETS exposure was 2.4 (95 percent confidence interval: 1.2, 4.5). Risk increased with both duration and quantity of exposure, with evidence of a linear trend. Cats with 5 or more years of ETS exposure had a relative risk of 3.2 (95 percent confidence interval: 1.5, 6.9; p for trend = 0.003) compared with those in nonsmoking households. These findings suggest that passive smoking may increase the risk of malignant lymphoma in cats and that further study of this relation in humans is warranted. In the same Journal, Drs. Reif, Dunn, Ogilvie and Harris published in 1992 (Volume 135(3):234-9) a case-control study to determine whether household exposure to environmental tobacco smoke was associated with an increased risk for lung cancer in pet dogs. Lung cancer cases and controls with other forms of cancer were obtained from two veterinary teaching hospitals during 1985-1987. Exposures assessed included the number of smokers in the household, the amount smoked, and the proportion of time spent indoors by the pet. A weak relation was found for exposure to a smoker in the home (odds ratio = 1.6, 95% confidence interval 0.7-3.7), after controlling for confounding in stratified analyses. Strong evidence for a further increase in risk associated with more than one smoker in the home was not found, nor was a significant trend observed for increasing number of packs of cigarettes smoked per day or an exposure index based on number of smokers in each household, packs smoked per day, and the proportion of time the dog spent within the home. However, skull shape appeared to exert effect modification; the risk was restricted to breeds with short and medium length noses (odds ratio = 2.4, 95% confidence interval 0.7-7.8). DOES PASSIVE HOUSEHOLD SMOKE CAUSE CANCER IN PET ANIMALS? The above studies provide compelling evidence that cats living in a household with a passive smoke environment have a 2.4 greater chance of developing lymphoma than cats in other households. The risk of lung cancer in dogs is not as profound. Whether passive smoke may lead to the development of other medical complications or other cancer conditions in dogs or cats is unknown. As with most retrospective studies in epidemiology, hindsight is 20/20 and limited questions give limited answers. For now, we will continue to observe the risks of passive smoke and cancer in humans as a model for the problems that may arise in our pets. SUGGESTED READING * Veterinary Oncology, From "The Practical Veterinarian Series". By Hahn KA. Butterworth-Heinemann Press, 2002. ======================================================================= Hope this info helps and don't hesitate to call us Gulf Coast Veterinary Oncology! Kevin A. Hahn, DVM, Phd, Diplomate ACVIM (Oncology), drhahn@gcvs.com Janet K. Carreras, VMD, Diplomate ACVIM (Oncology), drcarreras@gulfcoastvetspec.com Glen K. King, DVM, MS, Diplomate ACVR (Radiology & Radiation Therapy), drking@gcvs.com Gulf Coast Veterinary Diagnostic Imaging & Oncology 1111 West Loop South, Suite 150, Houston, TX 77027 P: 713.693.1166 F: 713.693.1167 W: www.gcvs.com