Can I be in danger of having breast cancer am 21 my aunt had breast cancer and my uncle died of cancer also my grandfather died of cancer?

Depends. Any woman is at risk for breast cancer. The average woman has about a 12% risk of getting breast cancer in her lifetime. You may be at increased risk if your first degree relatives have had breast cancer, ovarian cancer, or prostate cancer, particularly at a young age. See your doctor, who can better assess your individual level of risk.
you can not mix canc. Your aunt had b/ca but your g/f and uncle ca does not increase your chances for b/ca what kind of cancer they had? Your aunt ca may increase your risk check with your fdoc for screaning.