How much smoking actually causes cancer?
How much cigarette smoking causes lung cancer?
Turns out that a pack a day for five years is the critical tipping point where smokers are twice as likely as non- smokers to get lung, throat and larynx cancers.
This precedent- setting calculation figured prominently in Canada’s biggest class- action settlement, handed down Monday, awarding more than $ 15 billion in damages to smokers.
It is based on the expertise of Universite de Montreal epidemiologist Jack Siemiatycki, internationally known for research on occupational causes of cancer, who invented a way of measuring “critical dose” specifically for this case.
Monday’s judgment by Quebec Superior Court Justice Brian Riordan found three Canadian cigarette- makers liable for selling a harmful product they knew was dangerous while hiding those ill effects on health from consumers.
But that fault alone does not make a direct link between cigarettes and each individual smoker’s sickness.
The tobacco industry would have preferred that each member of the class action go to court to prove damages. But a million potential victims cannot individually parade through Riordan’s court, and that’s where Siemiatycki’s epidemiological analysis of probabilities came in.
Siemiatycki established a link between smoking and four diseases — emphysema, and lung, throat and larynx cancers — in his report.
According to the scientific literature, if no one smoked, 98 per cent of lung cancer would be eliminated, and up to 90 per cent of throat cancers too.
But how much cigarette smoke does it take to reach a “probability threshold” for each disease?
“My job in this case was to estimate where on the scale you have to be in order to get across the threshold of doubling the risk, and how many people in Quebec who get those diseases actually smoke that amount,” Siemiatycki said.
Siemiatycki turned to Statistics Canada surveys on smokers in Quebec for the combination of people who smoke, and dipped into the Registre des tumeurs du Quebec for a list of people with cancer; he then used an algebraic formula to calculate the critical carcinogen dose of “pack years” and relative risk of disease for the probability of smokers getting sick from smoking.
Experts hired by the tobacco industry tried to discredit Siemiatycki’s research as flawed but Riordan found it “reliable and convincing.”
For his part, Siemiatycki says he’s grateful to have been a critical part of the puzzle of this landmark trial.