Less Common Types of Breast Cancer

Although invasive ductal and lobular carcinomas account for about 90% of all breast cancer diagnoses, a number of breast cancer types are less common and include the following categories.
 

Medullary carcinoma is a type of infiltrating breast cancer that accounts for about 1-7% of all breast cancers.  Medullary carcinomas typically measure between 1 and 4 cms, and are characterized by large cancer cells, the presence of immune system cells throughout the tumor, and a rather well-defined boundary between the tumor and normal tissue.  These cancers generally have a better prognosis than most other breast cancer types, but are usually treated in the same way as invasive ductal carcinomas.

Inflammatory breast cancers account for 1-3% of breast cancer diagnoses.  They differ in that they usually do not present with a breast mass.  Instead, inflammatory breast cancers present as redness and warmth to the touch of the skin, and can cause the skin of the breast to develop a thick, pitted "orange peel" appearance.  The affected breast may become larger or firmer and feel itchy.  These symptoms are a result of the cancer cells blocking lymph vessels in the skin.  At times the diagnosis is confused with an infection of the breast, call "mastitis."  However, unlike mastitis, inflammatory breast cancer does not respond to antibiotic therapy.  Inflammatory breast cancer is often more aggressive and is typically treated with systemic therapy upfront, followed by surgery and radiation therapy. 

Mucinous carcinoma, also known as colloid carcinoma, is a rare type of invasive breast cancer, accounting for about 2% of invasive ductal carcinomas.  They are typically found in older women, being present in only 1% of women less than 35 years of age.  They usually present as a breast mass, with cancer cells surrounded by lakes of mucin.   This type of breast cancer is treated the same way as invasive ductal carcinoma, but has a much better prognosis than the more common invasive cancers.

Paget's disease accounts for 0.5 to 5% of all breast cancer.  It presents as a scaling, eczematous appearance of the nipple, typically crusted and red with areas of bleeding or oozing.  It is unknown whether the disease begins at the nipple or from the underlying breast tissue; however, it is estimated that over 90% of patients will have an underlying in situ or invasive cancer.  Treatment historically has consisted of mastectomy, but breast conservation therapy – which includes removal of the nipple areola complex – is an option for many women.

Papillary carcinoma can refer to either invasive or non-invasive forms of breast cancer.  Invasive papillary carcinoma accounts for only 2% of all breast cancer.  Under the microscope, the cells of these cancers are arranged in small, finger-like projections.  It is a rare cancer, occurring more often in older, non-Caucasian women, and is frequently associated with ductal carcinoma in situ.

Phyllodes tumor is a very rare breast tumor that develops in the stroma (connective tissue) of the breast.  It accounts for less than 1% of all breast tumors.  The typical age of presentation is mid 40s, however, they can be present in women from the age of 10 to the age of 80.  The majority of patients will present with a palpable mass of about 5cm, with a history of rapid growth.  Despite the large size, most phyllodes tumors are benign, with a low likelihood of being malignant. Surgery is usually the primary treatment for both benign and malignant phyllodes tumors, though occasionally radiation therapy may be used following surgery.

Tubular carcinomas are another type of invasive ductal breast cancers, and account for less than 2% of all invasive cancers.  "Tubular" refers to the appearance of the cells under the microscope.  They are treated the same as invasive ductal carcinomas, but have a better prognosis.

Metaplastic tumors account for less than 1% of all breast cancers.  These tumors are typically larger than other invasive cancers.  They are usually ER/PR negative (ER/PR-) and have a higher grade, but are less likely to spread to the lymph nodes.

Adenoid cystic carcinomas have both glandular and cystic features when seen under the microscope.  They make up less than 1% of breast cancers and rarely spread to lymph nodes or distant areas.  They typically present as a discrete palpable mass up to 3cm in size, beneath or around the areola. 

Angiosarcoma is a form of cancer that starts in the cells that line the blood vessels.  It can develop in any part of the body, but rarely in the breast.  When it does occur in the breast, it is usually as a complication or late effect of radiation therapy, developing 10-20 years after treatment.  It typically presents a bluish-purple-red discoloration of the overlying skin.  Overall, has a worse prognosis, requiring surgery for treatment.