A study reported in the Aug. 1 American Journal of Epidemiology (Vol. 156: 268-273) said second-hand smoke may increase the risk of malignant lymphoma in cats.

Study author Elizabeth R. Bertone, ScD, from the University of Massachusetts in Amherst, said this finding suggests study of the relationship between passive smoking and lymphoma in humans is warranted.

Malignant lymphoma is a common cancer in domestic cats and is similar to non-Hodgkin's lymphoma in humans, Bertone and her colleagues said in the report.

Recent studies have found that the rate of a common infection in cats with feline leukemia virus has declined, and experts believe this infection is not as likely linked to lymphoma in cats as once thought.

Bertone wanted to know if lifestyle and environmental factors influenced the disease risk in cats.

Bertone found that in households where cats were exposed to any second-hand smoke, they had more than double the risk of malignant lymphoma.

When cats were exposed for five years or more, the risk increased even further.

"Cats living in households in which a pack or more of cigarettes was smoked per day had a threefold increase in risk compared with cats with no household exposure," Bertone said.

The authors said they believe this is the first study to look at the association between household environmental tobacco smoke exposure and risk of malignant lymphoma in cats or other domestic animals.