Medullary cancer: This special type of infiltrating breast cancer has a rather well-defined, distinct boundary between tumor tissue and normal tissue. It also has some other special features, including the large size of the cancer cells and the presence of immune system cells at the edges of the tumor. Medullary carcinoma accounts for about 5% of breast cancers. The outlook, or prognosis, for this kind of breast cancer is better than for other types of invasive breast cancer. These are often hard to distinguish from invasive ductal carcinoma and are treated the same way. Most cancer specialists think that medullary cancer is very rare, and that cancers that are called medullary cancer should be treated as the usual invasive ductal breast cancer.

Metaplastic tumors: Metaplastic tumors are a very rare variant of invasive ductal cancer. These tumors include cells that are normally not found in the breast, such as cells that look like skin cells (squamous cells) or cells that make bone. These tumors are treated similarly to invasive ductal cancer.

Mucinous carcinoma: This rare type of invasive breast cancer is formed by mucus-producing cancer cells. The prognosis for mucinous carcinoma is better than for the more common types of invasive breast cancer. Colloid carcinoma is another name for this type of breast cancer.

Paget disease of the nipple: This type of breast cancer starts in the breast ducts and spreads to the skin of the nipple and then to the areola, the dark circle around the nipple. It is rare, accounting for only 1% of all cases of breast cancer. The skin of the nipple and areola often appears crusted, scaly, and red, with areas of bleeding or oozing. The woman may notice burning or itching. Paget disease may be associated with in situ carcinoma or with infiltrating breast carcinoma. If no lump can be felt in the breast tissue and the biopsy shows DCIS but no invasive cancer, the prognosis is excellent.

Phyllodes tumor: This very rare breast tumor develops in the stroma (connective tissue) of the breast, in contrast to carcinomas, which develop in the ducts or lobules. Phyllodes (also spelled phylloides) tumors are usually benign but on rare occasions may be malignant.

Benign phyllodes tumors are treated by removing the mass and a narrow margin of normal breast tissue. A malignant phyllodes tumor is treated by removing it along with a wider margin of normal tissue, or by mastectomy. These cancers do not respond to the usual treatments for invasive ductal or lobular breast cancer. In the past, both benign and malignant phyllodes tumors were referred to as cystosarcoma phyllodes.

Tubular carcinoma: Tubular carcinomas are another special type of invasive ductal breast carcinoma. It was named tubular because of the way the cells look under the microscope. Tubular carcinomas account for about 2% of all breast cancers and have a better prognosis than infiltrating ductal or lobular carcinomas. The majority of tubular cancers are hormone receptor positive but HER-2 negative.

Angiosarcoma: This cancer rarely occurs in the breasts. When it does, it is usually seen as a complication of radiation to the breast. It tends to develop about 5 to 7 years after radiation treatment. However, this is an extremely rare complication of breast radiation therapy. Treatment is the same as for other sarcomas Angiosarcoma can also occur in the arm of women who develop lymphedema as a result of lymph node surgery or radiation therapy to treat breast cancer.

Source: American Cancer Society