General breast cancer terms

It is important to understand some of the key words used to describe breast cancer.

Carcinoma This is a term used to describe a cancer that begins in the lining layer (epithelial cells) of
organs like the breast. Nearly all breast cancers are carcinomas (either ductal carcinomas
or lobular carcinomas).

Adenocarcinoma An adenocarcinoma is a type of carcinoma that starts in glandular tissue (tissue that
makes and secretes a substance). The ducts and lobules of the breast are glandular tissue
(they make breast milk), so cancers starting in these areas are often called
adenocarcinomas.

Carcinoma in situ This term is used for the early stage of cancer, when it is confined to the layer of cells
where it began. In breast cancer, in situ means that the cancer cells remain confined to
ducts (ductal carcinoma in situ) or lobules (lobular carcinoma in situ). They have not
grown into (invaded) deeper tissues in the breast or spread to other organs in the body.
Carcinoma in situ of the breast is sometimes referred to as non-invasive or pre-invasive
breast cancer.

Invasive (infiltrating) carcinoma An invasive cancer is one that has already grown beyond the layer of cells where it
started (as opposed to carcinoma in situ). Most breast cancers are invasive carcinomas -either
invasive ductal carcinoma or invasive lobular carcinoma.

Sarcoma Sarcomas are cancers that start from connective tissues such as muscle tissue, fat tissue,
or blood vessels. Sarcomas of the breast are rare.

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