Types of Breast Cancer

Breast cancer types are named according to the part of the breast in which they develop. The most common forms of breast cancer come from cells that line the milk ducts (ductal cancer) or the milk-producing lobules (lobular cancer).

In the early stages, cancer cells divide locally, and do not cross the wall of the duct or lobule. This type of cancer is called in situ—meaning “in place.” Once the cancer cells cross the lining of the duct or lobule, they are called infiltrating, or invasive. Do not be unduly alarmed if you are told your cancer is “invasive.” Most cancers are, so your invasive cancer is the “normal” cancer.

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Today about one in five cases of diagnosed breast cancers fall into the non-invasive, or in situ category—either ductal carcinoma in situ (DCIS), or lobular carcinoma in situ (LCIS).

DCIS cancers are highly curable. Some physicians don’t even refer to them as cancer, but rather as “precancerous lesions,” since DCIS may never progress to be an invasive cancer.

The treatment of DCIS may not follow the same plan as for invasive cancers, so we have dedicated a separate section to this non-invasive form of the disease. You still need to read the sections on staging, surgery and radiation to understand the principles involved.

LCIS is a non-invasive growth that is not considered cancerous, but women who are diagnosed with LCIS have about a 1% per year risk of developing invasive breast cancer. That means that twenty years after diagnosis, the risk is about 18%. What is important to know is that the invasive cancer can occur in either breast, and not necessarily where the LCIS was originally found. In other words, LCIS is not a precursor, but a marker.

Infiltrating or invasive cancers, where malignant cells cross the lining of the duct or lobule, are more advanced than in situ cancers. They invade, or infiltrate, adjacent tissues. The most common type of breast cancer is the infiltrating ductal carcinoma. More than half of all cases are of this type.

Other types of breast cancer are less common. One example is Paget’s Disease, a cancerous growth that first appears as scaling on the nipple, and may be confused for a simple rash. Another is inflammatory cancer, a rare form of cancer that grows quickly, and causes redness and swelling of the breast. This is really the only form of breast cancer in which the treatment decision needs to be made as soon as possible.