Classification of Breast Cancer Tumor Types

Histopathological classification of breast cancer establishes the diagnosis of the lesion, thereby aiding the determination of the patient treatment and their prognosis. Several pathological classifications mammary carcinomas are in used. The most commonly used are the Armed Forces Institute of Pathology (AFIP) and the World Health Organization. Breast carcinomas are classified as ductal or lobular, corresponding to the ducts and lobules of the normal breast. There is evidence that most tumors arise in the terminal duct section of the breast, regardless of the pathological type.

Carcinoma in situ

Tumors arising from the duct epithelium that are confined within the lumen of the ducts or lobules is called carcinoma in situ. Carcinoma in situ can be classified as ductal or lobular, depending on the cytologic features and patterns of growth. Ductal carcinomas in situ (DCIS), also known as intraductal carcinoma or noninvasive ductal carcinoma, and lobular carcinoma in situ (LCIS) are characterized by a proliferation of malignant epithelial cells confined to the mammary ducts or lobules. By light microscopy, no evidence of invasion throught the basement membrane of the surrounding stroma is seen. While the distinctions between DCIS and LCIS is usually obvious, overlaps exist.

Infiltrating Ductal Carcinomas

This category represents a variety of histological types of invasive (infiltrating) carcinomas. This includes infiltrating ductal carcinomas where no special histological features are designated NOS (not otherwise specified) and account for 70% of all breast cancers. This type is characterized by their stony hardness to palpation. When sectioned, a gritty resistence is sometime encountered. The tumor also may retract below the surface cut. Upon histological examination, fibrotic tissue and associated DCIS may be seen. These tumors commonly metastasize to the axillary lymph nodes, and their prognosis is the poorest of the various ductal types.

Medullary Carcinoma

Medullary carcinomas are circumscribed lesions of fairly large dimensions, demonstrating only low-grade infiltrative properties. They constitute 5-7% of all mammary carcinomas and are characterized by a well-circumscribed border, poorly differentiated nuclei, syncytial growth pattern, and an intense infiltration with small lymphocytes and plasma cells. The 5-year survival rate after treatment for this tumor type is better than for NOS ductal carcinoma. The more favorable prognosis requires the presence of all of these characteristics. Atypical medullary tumors do not have a favorable prognosis.

Tubular Carcinoma

A tumor with conspicuous tubule formation is seen is called a tubular or well-differentiated carcinoma. This diagnosis is made only if 75% or more of the tumor is composed of these elements. Axillary metastases are rare and the prognosis is considerable better than for NOS ductal carcinomas.

Mucinous Carcinoma

Mucinous or colloid carcinoma is another ductal type of tumor, accounting for 3% of all mammary tumors. It is slow growing and can reach bulky proportions. When the tumor is predominately mucinous, the prognosis is good. Rarer types of ductal carcinomas include papillary, adenocystic, apocrine, secretory, squamous, and carcinosarcoma or metaplastic duct carcinoma. In many cases, NOS ductal carciomas contain small regions of these special types.

Infiltrating Lobular Carcinomas

Infiltrating lobular carcinomas account for 5-10% of breast tumors, often presenting clinically as an area of ill-defined thickening in the breast. This differs from the usually dominant lump characteristic of ductal carcinoma. Microscopically, lobular carcinomas are composed of small cells in linear arrangements with a tendency to grow around ducts and lobules. Lobular carcinomas have a greater proportion of multicentric tumors in the same or opposite breast than are found in NOS ductal carcinoma. Overall, infiltrating lobular carcinoma has a similar likelihood of axillary node involvement and a similar prognosis as infiltrating ductal carcinomas. While ductal carcinomas often metastisize to bone or intraparenchymal sites within the lung, liver or brain, lobular carcinomas often show a predilection for meningeal and serosal surfaces.

Infiltrating Comedocarcinoma

Infiltrating comedocarcinoma is a type of infiltrating ductal carcinoma composed primarily of a comedo form of ductal carcinoma in situ. Comedo type is characterized by large poorly differentiated nuclei with frequent mitosis and central necrosis with areas of invasion. This term is out of favor, as it easily confused with pure comedo DCIS. Tumors with an extensive intraductal component appear to have important implications in breast-conserving treatment.

Paget's Disease

Paget's disease of the breast occurs in 1% of all patients with breast cancer. The patient presents with a relatively long history of eczematous changes in the nipple with itching, burning, oozine, bleeding, or some combination of these symptoms. The nipple changes are associated with an underlying carcinoma in the breast that can be palpated in half to two-thirds of the patients. The subadjacent tumor may be intraductal or invasive duct type. The prognosis is related to the histological type of the associated tumor. The nipple epidermis often contains tumor cells singly or in nests.

Inflammatory Breast Carcinoma

Inflammatory breast cancer is characterized by prominent skin edema, redness, and warmth, a visible erysipeloid margin, and induration of the underlying tissue. In approximately half of the patients, a palpable mass is not detected. These criteria in the past wree sufficient for a diagnosis. Currently, pathological corroboration is obtained by examination of a skin biopsy demonstrating involvement of the dermal lymphatics with cancer cells. Inflammatory cells rarely are present. The prognosis of patients with inflammatory breast cancer is poor, even if the disease is apparently localized.