The danger of cigarettes is mostly not in smoking them, argues a study by three doctors at the KS Hegde Medical Academy in Mangalore, India. Or, put another way: the danger comes from not smoking. Figuratively blowing smoke in the face of conventional wisdom, the study asks: "Are lung cancers triggered by stopping smoking?"

Arunachalam Kumar, Kasaragod Mallya and Jairaj Kumar take little for granted. They begin: "The clinically high correlation between smoking and carcinoma of the lungs has been the focal point in societal campaigns against the habit and the tobacco lobby." But their experience with patients suggests to them a different, seldom-told story. "We are struck by the more than casual relationship between the appearance of lung cancer and an abrupt and recent cessation of the smoking habit in many, if not most, cases."

Experience is their guide, numerically speaking. Of the 312 lung cancer patients they treated during a four-year period, 182 had recently quit smoking. The report goes into detail. "Each had been addicted to the habit no less than 25 years, smoking in excess of 20 sticks a day. The striking direct statistical correlation between cessation of smoking to the development of lung malignancies, more than 60% plus, is too glaring to be dismissed as coincidental."

One might quibble about this statistic - 182 cases out of 312 is 58%. In technical terms, one could accurately describe that as less than 60% minus. But it's still a startling number.

Kumar, Mallya and Kumar sketch out a possible explanation of what happens. There is, they surmise, a biological mechanism that protects smokers against cancer, that gets exercised and strengthened by years of diligent, heavy smoking. As in habitual marathon running, the body becomes accustomed to suffering grievous damage, and develops habitual ways to fix up whatever breaks down. The smoker's body becomes a sort of lean, puffing, self-damaging-yet-self-repairing machine.

But when a smoker gives up that regular regimen, the body cannot adjust. "It is our premise," say the doctors, "that a surge and spurt in re-activation of bodily healing and repair mechanisms of chronic smoke-damaged respiratory epithelia is induced and spurred by an abrupt discontinuation of habit, goes awry, triggering uncontrolled cell division and tumor genesis."

Things go downhill from there, in theory. The study appears in the journal Medical Hypotheses. In two pages, Kumar, Mallya and Kumar bleaken the already dire picture that research has painted about smoking cessation. The medically documented risks incurred by anyone who gives up cigarettes are well known. Depression, weight gain, irritability - these cruel fates have been written about time and again. Now add to them the risk of cancer, and the case against the case against smoking becomes even more persuasive.

At the very end of their paper, Kumar, Mallya and Kumar sum up their new view of things. "No doubt," they write, "tobacco kills too many. Or does it?"

· Marc Abrahams is editor of the bimonthly magazine Annals of Improbable Research and organiser of the Ig Nobel Prize