Breast cancer is a form of malignant cell growth that originates in tissues of the breast. The most common type of breast cancers are called ductal cancers (invasive ductal carcinoma), because the tumors begin in the lining of the milk ducts.However, the lining of thelobules, the glands that produce milk, is the site of origin of a less common form of breast cancer called invasive lobular carcinoma.
Breast tumors start small, posing the greatest danger if they remain undetected long enough to have the opportunity to grow and spread. If detected early, before spreading to lymph nodes and other surrounding tissues, the prognosis can be quite good. Breast cancer cases become much more serious or life-threatening once the malignant cells have begun to spread.