The affected cells and tissues then progress through multiple stages, with accompanying alterations in the surrounding tissue likely playing a role in whether the damage leads to a cancer.
These events contributing to subsequent cancers may occur spontaneously as a by-product of errors in normal processes, such as DNA replication, or potentially through effects of environmental exposures.
Although such biological “background” mutagenesis is unavoidable, highly efficient protective pathways, such as DNA repair and immune surveillance, are effective at reducing the impacts of procarcinongenic events (Loeb and Nishimura, 2010; Bissell and Hines, 2011).
Although more needs to be learned about both the mechanisms by which breast cancers arise and the array of factors that influence risk for them, much has been established.
The early procarcinogenic events from endogenous and exogenous processes may be sustained and furthered by physiologic conditions such as obesity.
It is likely that many such procarcinogenic events may never be entirely preventable because, although potentially modifiable, they are consequences of basic biologic processes, such as oxidative damage to DNA from endogenous metabolism, or stimulation of cell growth through normal hormonal processes. The decrease in breast-cancer incidence in 2003 in the United States.
Another 450 breast cancer deaths are expected among men in 2011 (ACS, 2011).
Since the mid-1970s, when the National Cancer Institute (NCI) began compiling continuous cancer statistics, the annual incidence of invasive breast cancer rose from 105 cases per 100,000 women to 142 per 100,000 women in 1999 (NCI, 2011). In 2008, the incidence of breast cancer was 129 cases per 100,000 women.
A portion of the decline in breast cancer incidence since 1999 is attributed to this reduced use of HT (e.g., Ravdin et al., 2007; Farhat et al., 2010).
But there are long-standing and still unresolved concerns that aspects of diet, ambient chemicals, or other potentially modifiable environmental exposures may be contributing to high rates of breast cancer.