Women who had smoked were at increased risk of breast cancer ( P = 0.007 ; HR = 1.3 for 15-35 years smoking , HR = 1.6 for 35 years ) , lung cancer ( P < 0.001 ; HR = 3.9 for 15-35 years , HR = 18.4 for 35 years ) , and colon cancer ( P < 0.001 ; HR = 5.1 for 35 years ) versus never-smokers .