A 60 year old woman comes worried to her family physician because she has noticed a lump in her right breast during self exam at home. She states that she had felt it initially about a month ago, but it has grown in size since then. She also states that she has had some bloody discharge from nipple. On breast exam, you are able to palpate a movable lump and you notice the skin of her breast is a little dimpled. You also detect some axillary Lymphadenopathy. What is the main risk factor for developing this condition?