Nevertheless, the research has been done - that means research under scientific conditions, eliminating as many variables as possible so that you know you're testing only that which you want to test - and no causative link could be found. This was such a shock to WHO that the numbers were massaged a little to show a link, and in that form the report forms the central tenet of every anti-smoking organisation on the planet, before they admitted the real results (following a court case).
It may seem logical to you that passive smoking causes cancer, but what is intuitive and what is true are often two completely different beasts. For instance, there's a proven link between circumcision and reduced risk of HIV infection. Intuitively this is nonsense, but it is true.
There is no proven causative link, despite studies into the phenomenon, between passive smoking and respiratory tract cancers. And the advice earlier in this thread is also true - if you don't want respiratory tract cancers, don't smoke. That's as near to a cure as you can get without actually being one.
