Most use a radial coordinate system, with nipple at the CENTER, and different radial orientation for each side, oriented as if you are FACING the patient:

12o'clock = top, 6o'clock = bottom, need CC, MLO, +/- ML views for precise clockface localization

Note that 3 o'clock is in the outer quadrant (OQ) on the left breast and in the inner quadrant (IQ) on the right breast

Should also give DISTANCE from nipple

Localizing a Lesion

diagram of clockface for both breasts