Cancer risk assessment: the science that is not

Print media coverage of research on passive smoking

OBJECTIVE

To assess the extent and content of newspaper and magazine coverage of research on passive smoking.

DESIGN

Content analysis of newspaper and magazine articles.

SUBJECTS

Articles reporting on passive smoking research published in newspapers (n = 180) or magazines (n = 92) between January 1981 and December 1994.

MAIN OUTCOME MEASURES

Numbers of articles, conclusions of articles, sources quoted, numbers and characteristics of research studies cited, presence of tobacco advertising.

RESULTS

The number of newspaper and magazine articles reporting on passive smoking research increased from four in 1981 to 57 in 1992 and 32 in 1994. Sixty-two per cent (168/272) of articles concluded that the research on passive smoking is controversial. Tobacco industry representatives were quoted significantly more often in newspaper articles (52%, 94/180) than magazine articles (12%, 11/92) (p<0.0001). Of 121 different research studies cited in the lay press articles, only 15 were from tobacco-industry sponsored projects or publications. In magazines, acceptance of tobacco industry advertising was associated with the conclusion that research on passive smoking is controversial (p<0.0001).

CONCLUSIONS

Although research on the harmful effects of passive smoking accumulated between 1981 and 1994, lay press coverage of the research maintained that the science was controversial. Few research studies were cited to support the industry's claim that passive smoking is not harmful to health. However, tobacco industry representatives who were critical of the research methods used to study the health effects of passive smoking were frequently quoted.

Expression of exposure in negative carcinogenicity studies: dose/body weight, dose/body surface area, or plasma concentrations?

Evaluation of positive findings in a rodent carcinogenicity study and the subsequent extrapolation to humans is based on chemical structure, mutagenicity, pharmacology, hormone changes, chronic toxicity, and the nature of the tumors induced. For negative studies, adequacy of exposure may become an issue. The use of plasma concentrations as a metric for exposure assumes that each species responds in a similar manner to a given concentration; data are now available that demonstrate that this is not generally true for carcinogenicity. The use of the body surface area metric (i.e., mg/m2) is a special case of interspecies allometric scaling (i.e., W0.67). For a chemical to be amenable to such scaling in toxicology, it must satisfy 3 criteria: (a) the concentration-time profile of the putative toxicant at the site of action must be governed by a scalable pharmacokinetic process (e.g., glomerular filtration); (b) the mechanism of action and the susceptibility of each species to a given systemic exposure must be the same and, for example, be independent of lifespan, cellular repair mechanism/rate, and so forth; and (c) the biological response must depend only on size (e.g., not on race, strain, gender, age, or parity). Carcinogens rarely, if ever, meet these criteria. An empirical analysis of carcinogenic potency data in rodents and in humans shows that, in general, exposure is best expressed in terms of mg/kg body weight.