Scientists at an influential state agency have completed a draft report linking second-hand smoke (search) to breast cancer, a finding that could lead air quality regulators to strengthen the state's indoor smoking laws (search).

It's the first major report to draw that connection, and one of many findings about the health effects of so-called environmental tobacco smoke, or ETS.

The 1,200-page report drafted by scientists at the Office of Environmental Health Hazard Assessment draws on more than 1,000 other studies of the effects of second-hand smoke and details a range of health problems caused by exposure to it. These included respiratory complications, heart disease and several cancers, many of which have been extensively documented.

But the report also establishes a connection between so-called passive smoking and breast cancer — a disease that kills about 40,000 women in the United States each year.

"The more recent primary, population-based case-control studies ... controlling for several important reproductive, dietary and other potential confounding factors, have consistently identified elevated breast cancer risks," the report concluded. "Overall, the weight of evidence ... is consistent with a causal association between ETS and breast cancer."

The report estimates that women exposed to second-hand smoke have up to a 90 percent greater risk of breast cancer than women who are not.

Agency spokesman Allan Hirsch said the conclusions in the report, particularly regarding breast cancer, had been based on several different studies that focused on the long-term effects of second-hand smoke, particularly in pre-menopausal women.

The report has been examined for several months and a scientific review panel could approve the findings as early as next Monday. The report would then be submitted to the Air Resources Board, which sets controls for air pollution in the state. If the board determines that second-hand smoke is a so-called toxic air contaminant, it can seek to regulate it.

Terry Pechacek, a spokesman for the Centers for Disease Control office on smoking and health, said in USA Today on Wednesday that the report will fuel a national debate on the link between smoking and breast cancer.

"I have to say without reservation it will stimulate continued and accelerated scientific evaluation of the smoking and breast cancer issue," Pechacek said.

In public comments to the board, Sanford Barsky, a UCLA researcher writing on behalf of the R.J. Reynolds tobacco company, said the report "either ignores mentioning or does not give the appropriate weight to studies which refute this association" between second-hand smoke and breast cancer.