I was pillow fighitng with my friend and his knee accidently hit my breast, i am worry because i am breastfeeding, can hit cause me a breast cancer ?

No: There have been some studies that propsed that trauma and the chronic inflamatory state that can follow from blood in the tissues, etc. May lead to carcinogenesis (new cancer growth) but at this point i think it is far from proven. There is excellent info on risk factors at http://www.Cancer.Org/cancer/breastcancer/index i would say it is very unlikely a knee to the breast would cause cancer.