''If people are serious about breast cancer, they have to deal with secondhand smoke. That's what this is all about," said Dr. Stanton Glantz, director of the Center for Tobacco Control, Research and Education at the University of California, San Francisco.
The report by scientists at California's Office of Environmental Health Hazard Assessment drew on more than 1,000 other studies of secondhand smoke and blamed the fumes for 4,000 deaths each year in California from lung cancer or heart disease alone.
The most significant new finding cited by state officials is that young women exposed to secondhand smoke increase their risk of developing breast cancer between 68 percent and 120 percent. The disease kills about 40,000 women in the United States each year.
That conclusion conflicts with a 2004 report by the US surgeon general. Sanford Barsky, a researcher writing on behalf of the R.J. Reynolds tobacco company, told the board the state report ''either ignores mentioning or does not give the appropriate weight" to studies denying a link between secondhand smoke and breast cancer.
California scientists say their research is more current than the surgeon general's report.
