“…The previous reanalysis of 53 epidemiological studies (Collaborative Group on Hormonal Factors in Breast Cancer, 2002), focusing on smoking status, also concluded that tobacco has no effect on overall risk of BC, but its effect on certain subgroups of women could not be excluded. Analysis of findings of the latter studies on this topic indicates that the link of smoking with BC may be dependent on several factors including age of smoking initiation, duration, amount of cigarette smoking per day, genotype, estrogen level, suggesting that early age at smoking initiation, longer duration of smoking and greater numbers of cigarettes are linked with increased risk (Hulka and Moorman, 2001;Reynolds et al, 2004;Gram et al, 2005;Olson et al, 2005;Terry and Goodman, 2006;Ha et al, 2007;Ahern et al, 2009;Pieta et al, 2009;Young et al, 2009;McKenzie et al, 2013). For example, Olson et al (2005) reported increased BC risk by 27% in women who started smoking before the first delivery and by 39% in those who started smoking between first menarche.…”