A 10-year study has found that adults exposed to second-hand smoke at home and in the workplace have a slightly higher risk of lung cancer, but it found no increased risk to children of smokers.Cancer experts say the study, done across Europe, indicates that passive smoking is a definite, although small, cause of lung cancer. The study was commissioned by the International Agency for Research on Cancer (IARC) and involved 650 patients with lung cancer and mroe than 1,500 healthy adults of "all ages" up to 74.