Passive smoking and lung cancer: current evidence and ongoing studies at the International Agency for Research on Cancer.

The evidence available from 3 cohort and 11 case-control studies investigating the relationship between exposure to environmental tobacco smoke (ETS) and lung cancer in non-smokers is reviewed. While it appears most likely that a causal relationship exists, the size of the effect, under different circumstances of exposures, remains to be accurately estimated. This requires studies using valid instruments (e.g., questionnaires) to quantitate exposures, and free as far as possible from biases. An investigation addressing this point is in progress under the coordination of the International Agency for Research on Cancer.