Smokers switching to low-tar, filtered cigarettes increase their chances of getting a type of cancer that strikes deep in the lungs, according to a study published Wednesday.
In research in the Journal of the National Cancer Institute, scientists say that the use of filter-tipped cigarettes with milder tobacco may be responsible for the increased rate of adenocarcinoma, a lung cancer which occurs in the small air sacs and tubes deep in the lungs.Dr. Clark W. Heath Jr. of the American Cancer Society, a co-author of the study, said that unfiltered cigarettes, which produce harsher smoke and larger particles, have been linked to cancers usually found in the lining of the upper pulmonary system.
"When filters were added to cigarettes and efforts were made to reduce the tar and nicotine, smokers needed to inhale more deeply to get the same amount of nicotine," said Heath.
This change in smoking habits, he said, may have caused adenocarcinoma to become the most common type of lung cancer.
In the study, researchers analyzed the types of lung cancer reported in the Connecticut Tumor Registry from 1959 through 1991. During that period, the deaths from adenocarcinoma in Connecticut increased from 0.9 to 15.2 cases per 100,000 person-years for women and from 2.4 to 23.2 cases per 100,000 person-years for men. A person-year represents one year of life for one person.
Heath said this increase parallels the introduction of filtered, low-tar cigarettes. It peaked among smokers who were born between 1930 to 1939, the group most likely to have started smoking the filtered cigarettes. The increase in women also tracked the increased use of filtered cigarettes by women, he said.
Earlier generations of smokers, he said, tended to have squamous cell or small cell lung cancers. These are cancers most commonly found in the lining of the larger air tubes within the pulmonary system, said Heath.
Until fairly recently, he said, adenocarcinomas were not considered a smoking-related cancer, but most researchers now believe the disease is linked to smoking.
Heath said the finding from the Connecticut data is consistent with other studies that have linked increased adenocarcinomas to filtered, low-tar cigarettes.