A California agency's decision to classify secondhand tobacco smoke as a risk factor for breast cancer has caused some conflict with some unlikely groups: antismoking organizations.

USA Today reported Feb. 1 that groups like the American Cancer Society, National Cancer Institute, and Centers for Disease Control and Prevention have thus far declined to endorse the conclusion of the California Environmental Protection Agency (CalEPA).

"At this point, there is not broad scientific consensus" linking secondhand smoke and breast cancer, said Michael Thun, vice president of epidemiology at the American Cancer Society. Thun issued a report on the CalEPA findings noting that breast cancer has not been linked with active smoking, much less passive smoking. "Lack of an association with active smoking weighs heavily against the possibility" of a secondhand-smoking link, Thun wrote.

Some explain the apparent logical inconsistency by theorizing that secondhand smoke and active smoking react differently with the female body.

"The scientific community is still watching for the evidence to evolve," said Jonathan Samet of Johns Hopkins University, the senior scientific editor of a report on secondhand smoking being prepared by the U.S. Surgeon General.

But Stanton Glantz, professor of medicine at the University of California-San Francisco, said the research on a link between secondhand smoke and breast cancer is actually stronger than the initial round of research on the link between secondhand smoking and lung cancer. 

"There are more studies, the risk estimates are more consistently elevated, and they're higher than they were for lung cancer," Glantz said. "Plus, there's all these toxicology studies and molecular biology they didn't have back then." Glantz called the position of the American Cancer Society and other groups "ridiculously conservative."