Guest Editorial: Lymphoma

Second-Hand Smoke May Be a Cause

Recently, a paper published in the American Journal of Epidemiology reported that cats whose owners smoke are up to three times as likely to develop lymphoma, a form of cancer, as cats living with nonsmokers. The researchers found that all cats exposed to tobacco smoke had a far higher risk of lymphoma, and that the risk was directly related to how much smoke was in the house and how long the cat had been exposed;  lymphomas were more likely when the length of time a cat was exposed to second-hand smoke increased, the number of smokers in the house increased, or the amount of cigarettes smoked in the house increased. We asked Rodney Page, DVM, director of the Comparative Cancer Center at the Cornell University College of Veterinary Medicine, to comment on the study…


Few factors have been identified as significant risks for the development of cancer in cats. It has been well established that feline leukemia virus and feline immunodeficiency virus infections are highly associated with the risk of lymphoma and leukemia. In addition, solar irradiation has been associated with skin cancer in the unpigmented sections of cats skin, particularly around the ears, eyes, and nose.

Thus, the importance of this study cannot be understated. First, the route of smoke exposure may be a result of direct inhalation or grooming behavior where cats ingest the smoke particles that settle on their fur. Particulates in cigarette smoke settle on many surfaces and cats, even those not in the immediate vicinity of cigarette smoke, may still collect these contaminants on their fur at later times.

The implication that reduction in second-hand smoke exposure may reduce the risk for lymphoma has not been definitively established but it seems obvious that the cats exposure to smoke should at the time be reduced. This can be accomplished by smoking cessation, restricting the smoke, cleaning furniture, rugs, and toys frequently, and bathing or cleaning the cat on a routine basis.

Another important implication is the potential for adverse effects of smoke on the development of other diseases. Previous studies in both humans and dogs have confirmed that second-hand smoke exposure increases the risk of nasal and lung cancer (different from lymphoma), as well as increased risks of other airway diseases such as asthma. It is also likely that second-hand smoke may increase the risk of these diseases in cats.

The human connection
According to one author of the study, Antony Moore, BVSc, head of the Harrington Oncology Program at the Tufts University School of Veterinary Medicine, Cats basically hang around inside the house, so they dont get exposed to as many possible environmental hazards, he said. You can often smell the smoke on their fur, and when you consider that theyre grooming all the time with their tongues, theyre probably getting a fairly significant dose.

It is important then to note that the oral exposure route proposed by the researchers in cats may be particularly relevant to small children in the house that mouth toys and other items which might be contaminated with smoke particles. As a public health tool, the health of family pets may be a useful means of communicating the dangers of tobacco use to children that could be more relevant than some of the methods currently employed.

Further study is warranted. It is necessary to examine direct causal links between smoke and cancer by measuring smoke byproducts in fur or tissue samples. In addition, this study creates new questions about how strategies to reduce risks to cats that live in smoking households can save lives – both feline and human!