Bullshit. I can find studies out the ass to support anything, and tons supporting the non-linkage between second hand smoke and cancer.
A family member onc's position on all this shit is "people with certain genetics can get cancer triggered by certain stimuli, but the studies fail to say YOU HAVE TO HAVE THAT GENETIC QUIRK."
Cross ref the people in these studies for certain mutations and you'll find they probably all had them. Yet these "studies" tell us "everybody who's around second hand smoke" is in danger of getting cancer. That's bullshit.
If second hand smoke were a legitimate cancer risk, as opposed to an infintessimally small one for a select group of people, think of how many people would have it.
These studies are almost always poorly written, but if you put it in the form of a paper, and claim you used the scientific method, somebody - shit, everbody - will believe you.