Know your family history
A first degree relative, that is, mother, sister, daughter that is diagnosed with premenopausal breast cancer can potentially put you at increased risk. If a first degree relative is diagnosed with breast cancer and you want to know what you should do- the following calculation can help: Take the age at which the first degree relative was diagnosed, subtract 10 years, and that is the age at which you should start annual screening mammography.
For example, if your sister was diagnosed at the age of 46 then you should start annual mammographic screening at the age of 36.
National recommendations for screening mammography in the ABSENCE of risk factors such as family history are yearly beginning at the age of 40.