If you haven’t noticed any abnormal features on breast self-examination like a breast lump, nipple discharge or skin changes, I would doubt that the pain
you are describing is associated to breast
cancer. The pain in
could be due to many benign causes like injury to the breast tissue, a pulled muscle, a pinched nerve, Costochondritis which is an inflammation of the cartilage that connects a rib to the breastbone and it could also be caused by an improper posture.