The breast is comprised of organs called lobules that can make drain and thin tubes called conduits that convey the drain from the lobules to the nipple. Breast tissue likewise contains lymph nodes, fat and connective tissue, arteries and veins. Breast cancer is a cancer that starts in the cells of the lobules or in the different tissues of the breast. The cancer may be of various types. Breast cancer that has spread from where it started in the pipes or lobules to encompassing tissue is called intrusive breast cancer. In incendiary breast cancer, the breast looks red and swollen and feels warm on the grounds that the tumor cells hinder the lymph vessels in the skin.

Targeted drug treatments attack specific abnormalities within cancer cells. As an example, several targeted therapy drugs focus on a protein that some breast cancer cells overproduce called human epidermal growth factor receptor 2 (HER2). The protein helps breast cancer cells grow and survive. By targeting cells that make too much HER2, the drugs can damage cancer cells while sparing healthy cells.