Do we know what causes breast cancer?

Do we know what causes breast cancer?

Many risk factors can increase your chance of developing breast cancer, but it is not yet
known exactly how some of these risk factors cause cells to become cancerous.
Hormones seem to play a role in many cases of breast cancer, but just how this happens is
not fully understood.
DNA is the chemical in each of our cells that makes up our genes—the instructions for
how our cells function. We usually look like our parents because they are the source of
our DNA. But DNA affects more than how we look.
Some genes contain instructions for controlling when our cells grow, divide, and die.
Genes that speed up cell division are called oncogenes. Others that slow down cell
division, or cause cells to die at the right time, are called tumor suppressor genes. Certain
changes (mutations) in DNA that “turn on” oncogenes or “turn off” tumor suppressor
genes can cause normal breast cells to become cancerous.
Inherited gene mutations
Certain inherited DNA changes can increase the risk for developing cancer and are
responsible for the cancers that run in some families. For example, the BRCA genes
(BRCA1 and BRCA2) are tumor suppressor genes. Mutations in these genes can be
inherited from parents. When they are mutated, they no longer suppress abnormal
growth, and cancer is more likely to develop.
Women have already begun to benefit from advances in understanding the genetic basis
of breast cancer. Genetic testing can identify some women who have inherited mutations
in the BRCA1 or BRCA2 tumor suppressor genes (or less commonly in other genes such
as PTEN or TP53). These women can then take steps to reduce their risk of developing
breast cancers and to monitor changes in their breasts carefully to find cancer at an
earlier, more treatable stage. These are discussed in later sections of this document.