Most cancers of the breast are invasive carcinoma, NST (no special type), frequently called invasive ductal carcinoma, which accounts for most cancers. The remaining cancers are referred to as "special type." The most common among the special types is invasive lobular carcinoma which is the second most common type after invasive carcinoma, NST. The remaining invasive cancers in the special type category are much less common and include the following (this list is not all-inclusive):
- Invasive lobular (ILC): This type of breast cancer accounts for approximately 10-15% of all invasive carcinomas in the breast. Most of these cancers are Nottingham grade I or II. An exception is so-called pleomorphic invasive lobular carcinoma. The cells of typical ILC grow in a characteristic pattern which distinguishes it from invasive carcinoma, NST. This growth pattern often makes it difficult to determine the actual size of the cancer by clinical exam or by radiology. These cancers are almost always estrogen and progesterone receptor positive and negative for HER-2 over-expression.
- Tubular: These are low grade breast cancers (Nottingham grade I) that are composed almost entirely of invasive duct-like structures that resemble normal breast ducts. It can sometimes be difficult for the pathologist to distinguish this type of cancer from benign lesions such as sclerosing adenosis or radial scar. Special studies or consultation with a breast pathologist can help with this distinction. These cancers are almost always estrogen and progesterone receptor positive and negative for HER-2 over-expression.
- Medullary: This is a rare type of breast cancer that has a very characteristic appearance under the microscope. These tumors are not graded using the Nottingham system as they are a unique cancer. There are very strict criteria that a pathologist must adhere to in making this particular diagnosis. These cancers are almost always negative for estrogen and progesterone receptors and negative for HER-2 over-expression.
- Mucinous: This is another breast cancer that has a very characteristic appearance--the cancer cells invade the breast tissue associated with abundant mucin. They can sometimes be confused with a benign finding called mucocele-like tumor. These cancers are almost always estrogen and progesterone receptor positive and negative for HER-2 over-expression.
- Adenoid cystic: This special type of breast cancer can be found arising in other parts of the body, particularly the head and neck area where they have a poor prognosis. However, in the breast, they tend to behave more favorably. These cancers are almost always negative for estrogen and progesterone receptors and negative for HER-2 over-expression.
- Invasive cribriform: This is another rare type of breast cancer that can sometimes be confused with ductal carcinoma in situ. Special studies or consultation with a breast pathologist can help with this distinction. These cancers are usually estrogen and progesterone receptor positive and negative for HER-2 over-expression.
- Invasive papillary: This is a special type of breast cancer where the cells grow in a characteristic form similar to papillary carcinomas that can be found in other organs, such as the ovaries and thyroid. Most of these rare cancers are estrogen and progesterone receptor positive and negative for HER-2 over-expression.
- Invasive micropapillary: This rare variant of breast cancer usually has a poor prognosis. The characteristic appearance of the cancer is the cells invading the breast tissue surrounded by "clear spaces". This type of breast cancer frequently spreads into the lymphatic spaces of the breast. Most of these cancers are positive for estrogen and progesterone receptors and approximately half or more are positive for HER-2 over-expression.
- Secretory: This very rare type of breast cancer tends to occur in younger women. These tumors tend to be circumscribed and the cells have a classic appearance under the microscope with abundant secretory material which helps distinguish this type of carcinoma from other types. The cancers are generally negative for estrogen and progesterone receptors and negative for HER-2 over-expression.