A California agency, the Air Resources Board, which first linked secondhand smoke to heart disease, now says secondhand smoke causes breast cancer too.
The researchers reviewed 13 studies and concluded that passive smoke causes breast cancer. The report has created controversy because other major health groups, including the World Health Organization, reviewed the same material but did not reach the same conclusion.
The California scientists gave more weight to animal studies and recent human studies that better screened women for exposure to tobacco smoke, but indicting secondhand smoke may be difficult because scientists haven't proven that active smoking causes breast cancer.
"As new studies come in, it's quite possible all these agencies will be persuaded this is rock solid. But this is the first to come to that conclusion,"said Dr. Michael Thun, a representative of the American Cancer Society.
Dr. Jonathan Samet, the senior scientific editor for Surgeon General's Report says some scientists are uncomfortable with the balance of evidence and not quite so convinced as the state of California that it's leaning strongly toward the positive.
Cigarette maker R.J. Reynolds claimed, in written comments, that the report is flawed.T hey claim the researchers made errors, misinterpreted data and sometimes failed to explain how they analyzed the data.
Tobacco company Philip Morris said they're still deciding whether to comment. The surgeon general's new report on secondhand smoke is due out later this year.