Surgeon General's Report Implicates Filtered Cigarettes in Increasing Cancer Risk

According to an article at Law360.com, the recently-released Surgeon General's report's conclusion that cigarette filters may actually increase the risk of lung cancer could lead to a new wave of class-action lawsuits against cigarette companies.

According to the article: "The U.S. surgeon general's landmark finding last week that filtered cigarettes may actually increase the risk of lung cancer could lead to a flurry of new lawsuits against tobacco companies and even expand cigarette litigation outside of Florida, where it has flourished for nearly a decade."

The Surgeon General's report concludes that: "The introduction of ventilated filters, or changes in the design and composition of cigarettes that accompanied their introduction, may have increased the carcinogenicity of cigarette smoke."

The introduction and proliferation of filtered cigarettes occurred mostly in the decades preceding and following the 1964 Surgeon General's report and was mostly complete by 1974. Further reductions in tar yield occurred through other mechanisms, as by 1974, most cigarette brands were filtered.

The Rest of the Story

While it is undeniably true that subsequent changes to the tar yield of cigarettes (changes subsequent to the introduction of filters) did not lower the lung cancer risk associated with cigarette smoking, one must be careful in concluding that the introduction of the filter resulted in an increase in lung cancer risk.

In fact, the bulk of the evidence suggests that the introduction of the cigarette filter, while obviously not making cigarettes substantially safer, did result in small but measurable declines in cancer risk. These declines occurred due to a tremendous reduction in tar yield, from levels as high as 40-50 mg down to less than 20 mg. The evidence suggests that further declines - to levels below this massive initial drop - were not associated with further declines in cancer risk.

Thus, it appears that cigarette filters did produce a small but measurable decline in cancer risks associated with smoking, while further design changes that lowered tar levels did not. In other words, there is evidence that filtered cigarettes produce lower cancer risks than non-filtered cigarettes. However, within the filtered cigarette category, there is no evidence that low-tar cigarettes confer any reduced cancer risk.

Unfortunately, the Surgeon General's report conflated these two types of changes and as a result, its conclusion that the introduction of the filter actually increased cancer risk is inaccurate and in conflict with the scientific evidence.

One of my first assignments at the Office on Smoking and Health at CDC was to evaluate the evidence regarding the relationship between changes in tar yield of cigarettes and the risk of lung cancer. I examined the literature regarding both the introduction of the filter and other design changes that subsequently led to very low tar yields. My conclusion was that the filter itself produced a massive decline in tar yields, so great that even with smoker compensation, the lung cancer risk declined. However, further declines in tar yields were apparently not sufficient to overcome compensation, and lung cancer risks did not decline any further. Thus, my conclusion was that the filter produced small but measurable declines in lung cancer risk, but low-tar cigarettes within the filtered cigarette category conveyed no decrease in lung cancer risk.

The scientific literature supporting the conclusion that filtered cigarettes are associated with a lower cancer risk than non-filtered cigarettes is substantial. I will not present the entire literature, but here are some representative studies:

Harris et al., in perhaps the most comprehensive and definitive study on this issue, found a clear increase in cancer risk associated with non-filtered cigarettes. As they reported: "Compared with smokers of medium tar (15-21 mg) filter cigarettes, risk was higher among men and women who smoked high tar (> or = 22 mg) non-filter brands (hazard ratio 1.44, 95% confidence interval 1.20 to 1.73, and 1.64, 1.26 to 2.15, respectively)."

Pogoda et al. found that the risk of acute myeloid leukemia is significantly higher among smokers of non-filtered compared to filtered cigarettes: "Odds ratios were significantly increased for ... subjects who smoked ... nonfiltered products (OR = 2.3, 95 percent CI: 1.1, 4.9)."

Sidney et al. found that among women, lung cancer risk was lower for lifelong smokers of filtered cigarettes than smokers of non-filtered cigarettes: "in long-term (> 20 years) smokers, the risk of lung cancer was decreased in women who had smoked filtered cigarettes for 20 or more years relative to lifelong smokers of unfiltered cigarettes (RR = 0.36, CI = 0.18-0.75)."

Falk et al., in a study of the risk for laryngeal cancer, found that: "Higher risks were associated with smoking nonfiltered than filtered cigarettes." For those who smoked filtered cigarettes, the OR was 5.9 (95% CI = 2.4-14.4); for those who smoked non-filtered cigarettes, the OR was 9.0 (95% CI = 3.2-25.1). 

Luchtenborg et al. found that while non-filtered cigarettes increased the risk for colon cancer (OR 1.59; 95% CI, 1.15-2.21; P(trend) = 0.001), filtered cigarettes did not increase colon cancer risk (OR 1.05; 95% CI, 0.79-1.39; P(trend) = 0.98).

Wynder et al. reported slightly lower bladder cancer risk among filtered cigarette smokers: "Smokers of filtered cigarettes had a slightly reduced risk of bladder cancer relative to smokers of nonfiltered cigarettes (odds ratio 0.64, 95% confidence interval 0.38 to 1.10 among male smokers; odds ratio 0.74, 95% confidence interval 0.37 to 1.48 among female smokers)."

Hartge et al. found exactly the same result as Wynder's group: "Our data indicated that people who have only smoked unfiltered cigarettes have higher risks."

Sadly, although the Surgeon General's report draws conclusions about the health impact of filtered cigarettes, it only cites one of these seven studies (the Luchtenborg study). And in citing that study, the report merely notes its finding that smoking increases colon cancer risk. It hides this study's finding that this increased colon cancer risk was only detected among smokers of non-filtered cigarettes!

Why does the Surgeon General's report not review the literature on the cancer risks of filtered vs. non-filtered cigarettes, even though it seems to draw a conclusion about this issue? The only answer I can think of is that the report aimed to draw a particular conclusion, rather than to present the facts in an objective way. Apparently, the report was pre-determined to conclude that all design changes to cigarettes increased their cancer risk. It conflated the filter with other sources of tar yield reductions and at the same time, failed to review studies that examined the relative risk of filtered vs. non-filtered cigarettes.

As a result, the report implies that cigarette filters increase lung cancer risk and opens the way for lawsuits based on this claim, as the Law360.com article suggests.

But the truth is more nuanced. While there is no question that low-tar or "light" cigarettes are not safer, it is not the case that the introduction of filters made cigarettes more carcinogenic. I would not be able to testify in a courtroom that I believe filtered cigarettes are more dangerous than non-filtered cigarettes. Nor would I be able to testify that filtered cigarettes and non-filtered cigarettes pose equivalent cancer risk.

It is important to point out that just because the relative risk of cancer associated with filtered cigarettes is lower than that for non-filtered cigarettes, it does not necessarily follow that switching from a non-filtered to a filtered cigarette will reduce one's health risks. It is possible that smokers who make such a switch will compensate because they are used to higher tar levels. It is possible that the observed reduction in cancer risk only holds for lifelong filtered cigarette smokers, as they do not compensate (they never smoked non-filtered cigarettes). In fact, the scientific evidence supports this contention.

The rest of the story is that in yet another area of tobacco control science, the Surgeon General's report is providing a biased view of the scientific evidence.