The background population risk of developing breast cancer in your lifetime is 1 in 8 and this will not change much whether you take HRT or not.
There are aspects of your medical history and lifestyle that can increase your background risk of developing breast cancer, usually by only a very small degree. Some of these factors are things we can influence ourselves (weight, alcohol) and others are things we cannot change (family history of cancer, genetics).
Even if you have these risk factors, the chance of developing breast cancer is still small and most women who have some of the above risks will not develop breast cancer in their life.
The increased risk of developing breast cancer associated with taking HRT is understandably a very common concern that women mention when they come to our clinic to discuss HRT.