Under normal circumstances, breast gland epithelial cells divide and grow in an orderly fashion. But at some point, for some reason, some cells undergo genetic mutation and the cells proliferate out of control, showing disorderly and unrestricted malignant division and growth, thus evolving into adenocarcinoma cells. A large number of cancer cells proliferate and crowd into a mass in a disorderly manner, squeeze and erode and destroy the surrounding normal tissues and damage the normal structure of the breast, then gradually breast cancer is formed. Therefore, breast cancer is a malignant tumor that occurs in the glandular epithelial tissue of the breast and is one of the most common malignant tumors in women. Many breast cancers begin as tumors on the surface cells of the milk ducts, while others develop as tumors on the lobules of the breast. Breast cancer includes two main types of cancer: invasive carcinoma of the breast and carcinoma in situ of the breast.