In addition to the type, the cancer can be non-invasive, which means it does not spread beyond the lobule or duct, or invasive, which means it has spread beyond the lobule or duct. (See diagram below)

Types of Non-Invasive Breast Cancer

Ductal Carcinoma In Situ (DCIS)

DCIS is the most common type of non-invasive breast cancer and is sometimes called intraductal carcinoma. It is malignant (cancerous), and as it grows, the center of the tumor starts to die because it has outgrown its blood supply. This area of dead tissue, called necrosis, can calcify, which can be detected on a mammogram. DCIS tumors are further identified by how the cells appear under the microscope, classifying them into subtypes. These subtypes are comedo, papillary, micropapillary, solid and cribiform. Many tumors will represent a combination of two or more subtypes. In general, all types of DCIS are treated similarly. (See diagram of DCIS below)

Lobular Carcinoma in Situ (LCIS)

LCIS lesions rarely develop necrosis or calcifications, so are not often detected on mammograms. LCIS is not considered a true cancer, rather an accumulation of abnormal cells in the lobule. It is considered a risk factor for developing breast cancer in the future in either breast. LCIS is often found incidentally by the pathologist in a tissue specimen that was removed for another reason.

Types of Invasive Breast Cancers

Infiltrating Ductal Carcinoma (IDC)

IDC is the most common type of invasive cancer, accounting for about 85% of cases. This tumor starts in the duct and spreads beyond the duct into normal breast tissue.

Infiltrating Lobular Carcinoma (ILC)

ILC is less common, accounting for about 5-10% of cases. This tumor starts in the lobule and extends beyond the lobule into normal tissue.

Medullary Carcinoma

Medullary carcinoma is rare, accounting for only 5% of all breast cancers, and carries a very good prognosis. These cancers typically have a well defined boundary between the cancer cells and the normal cells. Of note, this type of cancer will not be given a histological grade by the pathologist (discussed below).

Inflammatory Breast Cancer ( IBC )

IBC is also rare, accounting for 1-4% of breast cancer cases, and presents differently from other types of breast cancer. Common symptoms include swelling or enlargement of one breast, reddened, warm to the touch, itchy and tender skin, typically without a lump. In some cases, the skin becomes thickened and dimpled, appearing like an orange peel, giving this sign the name "peau d'orange". IDC tends to be an aggressive form of breast cancer.

Tubular Carcinoma (TC)

TC is a rare type of invasive breast cancer, accounting for about 2% of cases. Its name comes from the pathologist seeing a "tubular pattern" in 75% or more of the specimen. TC does not typically spread to other areas of the body (called metastasize) and is associated with very good prognosis.

Mucinous Carcinoma (MC)

MC may also be called colloid carcinoma and is a slow growing tumor. This tumor is also rare and is named for the mucin (protein and sugar compound) produced by and surrounding the tumor cells. These tumors also rarely spread to other parts of the body (metastasize) and also carry a very good prognosis.

Other Rare Subtypes

* Metaplastic – a rare variation of IDC

* Adenoid Cystic – rare variation of a tumor that more commonly occurs in the salivary gland

* Papillary

* Secretory

* Paget's Disease: development of red, weeping or crusty lesion on the breast tissue or nipple. While not a cancer itself, this is associated with an underlying breast cancer.