Types of Breast Cancer

Different types of breast cancer may be treated differently or have a different prognosis, so it is helpful to understand how they differ. These differences are primarily based on the pathology of the tumor. This cannot be definitively determined until some tissue from the breast cancer, a biopsy, is taken and evaluated by a pathologist. The pathology report will explain which type of cancer was found.

Common Types of Breast Cancer

Most breast cancers arise from the cells lining the milk ducts in the breast (ductal carcinoma) or in the gland tissue that produces the milk (lobular carcinoma).

In Situ Breast Cancer: In situ means that the cancer cells have not invaded from their original position where they developed. They have not yet eroded into the surrounding breast tissues. Therefore they are considered noninvasive cancers. The most common type is called ductal carcinoma in situ (DCIS) which originates from the milk ducts and has so far remained within the duct. These cancers can become invasive with time and progress to more invasive types of breast cancer. But if breast cancer is diagnosed at this early stage, the prognosis with treatment is generally very good.

Invasive Breast Cancer: Invasive or infiltrating breast cancers have spread and invaded through the tissue layers surrounding the milk ducts or glands. They have eroded into and are growing in surrounding tissues and can then start to spread to distant sites in the body including the lymph nodes and then other organs.

The most common type of invasive cancer of the breast is invasive ductal carcinoma (IDC). These cancers arise from the cells lining the milk ducts but have grown through into the surrounding breast tissues. Less common is the invasive lobular carcinoma (ILC) which starts in the cells of the milk-producing glands.

Less Common Breast Cancer Types

The types of breast cancer discussed above are the most common by far. However, there are a number of different cancers that can rarely affect the breast.

Metastatic Cancers to the Breast: Some cancers can spread to distant organs in the body. Rarely a cancer from another organ can spread to the breast. These are not technically breast cancer but rather are named for the organ or tissue from which they originated.

Inflammatory Breast Cancer: Inflammatory breast cancer is a rare form that is very aggressive. Unlike other types of breast cancer, it is outwardly visible because the breasts become swollen and red, due to invasion of the lymphatic vessels in the breast. The skin can become pitted or wrinkled similar to the skin of an orange (this appearance is called peau d'orange. The prognosis is generally poorer than most other types because it has often become invasive or metastasized by the time it is diagnosed.

Phyllodes Tumor: Another rare form, phyllodes is a fast-growing tumor that originates from the cells around the ducts in the breasts.

Adenoid Cystic Carcinoma: A rare form of adenocarcinoma which can occur in the breast.

Paget's Disease of the Breast: Another rare breast cancer starts in the breast ducts but spreads quickly down the ducts to the skin of the nipple and the surrounding dark tissue (called the areola). This is considered a variant of invasive ductal carcinoma.

Rare Subtypes of Invasive Ductal Carcinoma: There are other rare subtypes of invasive ductal carcinoma which can be classified as tubular, mucinous, medullary or papillary.

Other Ways that Breast Cancers are Classified

Tumor Grade: The grade of a tumor refers to how abnomal the cells are. Higher grades are tumors whose cells least resemble the normal cells that they originated from. They tend to be more aggressive and invasive. Breast cancers are graded on a scale from 1 to 3. Grade 1 have relatively normal appearing cells (well differentiated) while Grade 3 has very abnormal cells (poorly differentiated). Grade 2 is somewhere inbetween. The grade of the tumor has an impact on treatment options and ultimate prognosis.

Hormone Receptor Status: Hormone receptors are proteins which detect blood-borne signals from hormones and cause some change in the cell. Most breast cancers are routinely tested for the presence of specific types of receptors to estrogen and progesterone, the hormones of the female reproductive system. Cancers that are negative for the hormone receptors tend to be more aggressive and grow faster. Those that are positive for hormone receptors tend to grow more slowly. They may also be treated by medications that block the hormone receptors, such as tamoxifen, which further slows the tumor's growth.

Gene Typing (HER-2 Status and Others): Some genes that are expressed by breast cancers are used to classify them and can help guide treatment. For example, HER-2 is a protein produced in some breast cancers more than others. Tests can be performed to determine if the gene for this protein is increased in a given cancer. Tumors that are positive for HER-2 can sometimes be treated with special drugs that target the protein, such as Herceptin (trastuzumab) and Tykerb (lapatinib). Other newer ways to classify types of breast cancer include Luminal A and Luminal B.