Many longtime smokers quit spontaneously with little effort shortly before their lung cancer is diagnosed, leading some researchers to speculate that sudden cessation may be a symptom of lung cancer.

Most patients who quit did so before noticing any symptoms of cancer, according to the study, which was published in the March issue of the Journal of Thoracic Oncology (JTO), the official monthly journal of the International Association for the Study of Lung Cancer (IASLC).

"It is widely known that many lung cancer patients have stopped smoking before diagnosis," said Dr. Barbara Campling, professor in the Department of Medical Oncology at Thomas Jefferson University in Philadelphia. "This observation is often dismissed, by saying that these patients must have quit because of symptoms of their cancer. However, we found that the majority of lung cancer patients who stopped smoking before diagnosis quit before the onset of symptoms. Furthermore, they often quit with no difficulty, despite multiple previous unsuccessful quit attempts. This has led us to speculate that, in some cases, spontaneous smoking cessation may be an early symptom of lung cancer."

Researchers interviewed 115 lung cancer patients from the Philadelphia Veterans Affairs Medical Center, all of whom had been smokers. Fifty-five (48%) had quit smoking before diagnosis, and only six of those (11%) had experienced symptoms of lung cancer by the time they quit. Patients with lung cancer who quit were as dependent on nicotine, when their smoking was at its highest point, as those who continued to smoke. Yet 31% reported quitting with no difficulty.

For comparison, researchers also interviewed patients with prostate cancer and those who had suffered a heart attack. They found that the median interval between quitting smoking and lung cancer diagnosis was 2.7 years. This compared with 24.3 years for prostate cancer and 10 years for a heart attack.

Researchers speculated that spontaneous smoking cessation may be a presenting symptom of lung cancer, possibly caused by tumor secretion of a substance interfering with nicotine addiction.

The results should not encourage smokers to continue smoking, Campling said.

"There is a danger that this study could be misinterpreted as suggesting that heavy smokers should continue smoking," Campling said. "We emphasize that all smokers must be strongly encouraged to stop."

The research was supported by a grant from the Veterans Affairs Healthcare Network Competitive Pilot Project.