The study, still ongoing, compared family histories of cancer in the immediate families of 806 lung cancer patients with that of a group of 663 control families, and provides indirect evidence that variation in individual susceptibility to smoking and cancer may be genetically-determined.
Aggregation of cancer in families can be due to shared exposures, shared genes, or a combination of both, says Carol Etzel, Ph.D., a statistician and instructor in the Department of Epidemiology. Previous studies at M. D. Anderson and other institutions have found similar results.
"Only about 15 percent of all smokers develop lung cancer, and in families of those smokers, our belief is that it is more likely other family members will be just as susceptible if they also smoke," says Etzel. "We all are familiar with someone who smoked for years and never got cancer, while another person who didn't smoke much developed the disease. It is those individual differences, expressed in genetic tendencies, that we are exploring."
In all, the study ascertained family cancer history in 6,430 first-degree relatives (parents, siblings and offspring) of patients, and 5,505 relatives of control subjects.
The researchers interviewed patients and control participants, asking detailed questions about their smoking habits and those of their families, and whether any family members had developed smoking related cancers, such as lung, bladder, kidney, head and neck, and pancreas. Most of the cancer patients were over the age of 60 and were current or former smokers, Etzel notes, so the issue of second hand smoke was not a factor.
They found that there was a nearly two-fold increased risk of lung cancer among relatives of smokers, but no evidence of an increased risk among relatives of people who never smoked.
If the genes responsible for susceptibility to developing lung and other smoking-related cancers are found, it may be possible to identify high-risk subgroups of smokers and to develop tailored interventions or screening programs, says Etzel.
Possible genes that may affect a smoker's risk of developing cancer are being intensively studied, she says, including genes that help to detoxify the cancer causing agents in tobacco smoke - and so confer a protective effect - as well as genes that effect the ability to repair genetic damage, and thus to prevent the negative biological consequences of smoking.