Breast cancers are classified according to the cell type in which the disease begins. Most breast cancers begin in cells that line the ducts that carry breast milk to the nipple, or in the glands that produce breast milk.
(Lobular carcinoma in situ, or LCIS)
In this condition, abnormal cells are found in the lobules, but they have not spread. Lobular neoplasia is not considered a true cancer, and does not usually require treatment. However, it can be an indication that a woman faces higher than average risk for developing breast cancer later on.
These cancers have not spread from their original site into surrounding breast tissue.
Ductal carcinoma in situ (DCIS)
Also called Stage 0 breast cancer, DCIS means that cancer cells are found only in the cells that line the ducts. Many cases of DCIS will never spread or become invasive, however because there is no reliable way to determine which cases will spread and which ones won’t, almost all women with DCIS are treated.
These cancers have spread into surrounding breast tissue, and can travel to lymph nodes and metastasize to distant areas of the body.
Invasive Ductal Carcinoma (IDC)
About 8 out of 10 invasive breast cancers are ductal carcinoma, which begins in the cells that line the milk ducts in the breast, and spreads through the duct wall and into nearby breast tissue.
Invasive Lobular Carcinoma (ILC)
Far less common, this breast cancer type begins in the glands (lobules) that produce breast milk. About 1 in 10 invasive breast cancers are lobular carcinoma.
Subtypes of these invasive breast cancers are classified according to cell features that are seen under the microscope. These subtypes are rare, and collectively account for less than 5% of all breast cancers.
- Adenoid cystic carcinoma
- Low-grade adenosquamous carcinoma
- Medullary carcinoma
- Papillary carcinoma
- Tubular carcinoma
- Metaplastic carcinoma
- Micropapillary carcinoma
- Mixed carcinoma (show features of both ductal and lobular)
Inflammatory breast cancer
Inflammatory breast cancer is characterized by swelling and redness in the breast, inverted or retracted nipple, and thickening or pitting of the breast skin that resembles orange peel, and may be itchy. This rare breast cancer type tends to be more aggressive and is often diagnosed at later stages, when treatment is more difficult.
Paget disease of the nipple
This rare breast cancer type begins in the breast ducts and spreads to the skin of the nipple and areola, oftentimes affecting both breasts. The skin may become red, scaly and itch. Sometimes Paget disease spreads beyond the nipple and is treated similarly to other invasive breast cancers.
Phyllodes tumor develops from cells in the connective tissue, or stroma, rather than inside the milk ducts or glands. These tend to grow quickly, producing a breast lump, but not all of these are malignant. Many are benign (noncancerous), and some are considered borderline. Accurate diagnosis is essential.
Angiosarcoma of the breast
Angiosarcoma of the breast begins in cells that line the blood or lymph vessels. Although rare, this cancer type sometimes results from previous breast cancer radiation treatment.