Breast cancer definition: Cancer which is formed in breast tissues usually in the ducts (ducts that used to carry the milk to nipples) and lobules (glands, which make milk).Its occurrence is common in both male and female, although breast cancer in males is rare.In US new cases for breast cancer in females and males are 192,370 and 1,910 respectively while the death rate in female is 40,170 and in male is 440. Read more »