What is breast cancer?

What is breast cancer?
Cancers are a group of diseases that cause cells in the
body to change and grow out of control. Most types of
cancer cells eventually form a lump or mass called a
tumor and are named after the part of the body where
the tumor originates.
Breast cancer begins in breast tissue, which is made up
of glands for milk production, called lobules, and the
ducts that connect lobules to the nipple. The remainder
of the breast is made up of fatty, connective, and
lymphatic tissue.
• Most masses are benign; that is, they are not
cancerous, do not grow uncontrollably or spread, and
are not life-threatening.
• Some breast cancers are called in situ because they are
confined within the ducts (ductal carcinoma in situ) or
lobules (lobular carcinoma in situ) of the breast. Nearly
all cancers at this stage can be cured. Many oncologists
believe that lobular carcinoma in situ (also known as
lobular neoplasia) is not a true cancer but an indicator
of increased riskfor developing invasive cancer in the
future.
• Most cancerous breast tumors are invasive, or infiltrating.
These cancers start in the lobules or ducts of the
breast but have broken through the duct or glandular
walls to invade the surrounding tissue of the breast.
The seriousness of invasive breast cancer is strongly
influenced by the stage of the disease – the extent or
spread of the cancer when it is first diagnosed. There are
two main staging systems for cancer. The American Joint
Committee on Cancer’s classification of tumors uses
information on tumor size (T), lymph node involvement
(N), and the presence or absence of distant metastases
(M), and is commonly used in clinical settings.1 Once the
T, N, and M are determined, a stage of I, II, III, or IV is
assigned, with stage I being an early stage and stage IV
being the most advanced.