Bruises are almost never a sign of underlying cancer. A bruise
is actually just blood that has escaped the blood vessels because of trauma. Sometimes the trauma that occurs is not noticed and a bruise appears without the person remembering why or how it happened. Breast cancer is usually causes a lump that can be felt on a breast exam. Sometimes the lump is too small to feel, but can be seen on a mammogram
of the breast. In rare cases, a breast cancer can cause the overlying skin to turn orange or dimple. Sometimes the nipple becomes inverted because of an underlying cancer. Bruises however are not a sign.
With that said, you should have a breast exam every year by your physician to be sure that there are no lumps or other findings that need further examination. I suggest that you schedule an appointment for this purpose. In addition, you should start getting mammograms every year sometime between the ages of 40 and 50 depending on your family history and your physician's preference. If you have a strong family history of breast cancer, you may need screening breast MRIs prior to the age of 40. I hope that helps.