Association Between Passive Smoking and Cancer in Pets

Dr. Robyn Elmslie DVM
Dr. Phyllis Glawe DVM

One of the most common questions asked by owners of cancer-bearing pets is whether or not there is an environmental factor that might have caused their pet's cancer. Over the past decade, two types of cancers, lymphoma in cats and primary lung cancer in dogs have been particularly scrutinized for their association with their pet's exposure to passive inhalation of cigarette smoke. Results of two studies are outlined below.

Lymphoma in Cats: In the summer of 2002, the American Journal of Epidemiology reported a retrospective study about the risk(s) of malignant lymphoma in pet cats in households with second-hand smoke exposure. Several studies have suggested that smoking may increase the risk of non-Hodgkin's lymphoma in humans. 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 during the two 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. Cats with 5 or more years of ETS exposure had a relative risk of 3.2 compared with those in nonsmoking households. These findings reveal that passive smoking may increase the risk of malignant lymphoma developing in cats.

Primary Lung Cancer in Dogs: In 1992, the American Journal of Epidemiology reported 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 association was found for exposure to a smoker in the home. This risk of developing lung cancer was not increased with more than one smoker in the home, 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. This study revealed that exposure to environmental smoke does not significantly increase the risk of pet dogs developing primary lung cancer. observe the risks of passive smoke and cancer in humans as a model for the problems that may arise in our pets.