A link between a common cancer in household cats and the smoking habits of their owners has researchers concerned and urging further study into a possible connection between non-Hodgkin's lymphoma in humans and second-hand tobacco smoke.
In a study being reported Wednesday in the American Journal of Epidemiology, researchers at the University of Massachusetts at Amherst and Tufts University in Boston found that a cat's risk of developing feline lymphoma, the most common cancer in cats, doubled if it shared a home with a smoker, and increased fourfold if it lived with two smokers. The risk for cats living with a person who smokes a pack of cigarettes or more a day tripled, compared with cats living with non-smokers.
Lead author Elizabeth Bertone, an epidemiologist at the University of Massachusetts, says the finding in cats may signal a similar risk to children.
''Often studying these exposures in pets can tell us about their effects in humans,'' she says. Malignant lymphoma in cats is ''fairly similar in cell type and distribution'' to non-Hodgkin's lymphoma in humans, she says. Both diseases can occur at any age, but incidence tends to peak late in life -- age 10 for cats and about 70 years of age for humans.
Cats, especially those that live indoors all the time, share breathing space with humans, and, like children mouthing toys, may consume smoke particles while grooming their fur.
Passive smoking hasn't been studied in humans with non-Hodgkin's lymphoma, Bertone says, but some studies have found the risk among active smokers is two to three times that of non-smokers, though studies are not consistent.
Non-Hodgkin's lymphoma in humans, like feline lymphoma, is a cancer that starts in lymph tissue and can spread to other organs. The new study suggests that components of tobacco smoke may have a cancerous effect on lymphoid tissue, researchers say.
This is not the first study to link passive smoke and cancer in pets. In 1992 and 1998, John Reif of Colorado State University's College of Veterinary Medicine and Biomedical Sciences reported that dogs that live with smokers have higher rates of both lung and nasal cancers.
''It's a big issue for pet owners,'' Reif says. It may help animal-loving smokers to quit. ''If they're not interested in their own health, maybe they'll do it for their pets.''
Study Abstract (Summary)
Environmental Tobacco Smoke and
Risk of Malignant Lymphoma in Pet Cats
Am J Epidemiol 2002; 156:268-273.
Copyright © 2002 by the Johns Hopkins Bloomberg School of
1 Department of Biostatistics and Epidemiology, School of Public Health and Health Sciences, University of Massachusetts,
2 Department of Clinical Sciences, Tufts University School of Veterinary Medicine, North Grafton, MA.
3 Harrington Oncology Program, Tufts University School of Veterinary Medicine, North Grafton, MA.
Feline malignant lymphoma occurs commonly in domestic cats and may serve as a model for non-Hodgkin's lymphoma in humans. Several 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. Am J Epidemiol 2002;156:268-73.
Key Words: cat diseases; lymphoma; smoke; smoking; tobacco smoke pollution
Abbreviations: CI, confidence interval; ETS, environmental tobacco smoke; TUSVM, Tufts University School of Veterinary Medicine.