Types of Breast Cancers

Histologic examples of in situ & invasive carcinomas of the breast

Breast cancers can be divided into two main overarching groups: the carcinomas and the sarcomas. Carcinomas are cancers that arise from the epithelial component of the breast. The epithelial component consists of the cells that line the lobules and terminal ducts; under normal conditions, these epithelial cells are responsible for making milk. Carcinomas comprise the vast majority of all breast cancers, and will be further discussed below. Sarcomas are rare cancers that arise from the stromal (connective tissue) components of the breast. These stromal component cells include myofibroblasts and blood vessel cells, and cancers arising from these "supportive" cells include phyllodes tumors and angiosarcoma. Sarcomas account for less than 1% of primary breast cancers.

Within the large group of carcinomas, there are many different types of breast cancer. The first major division is between in situ and invasive carcinoma. In situ carcinoma is "pre-invasive" carcinoma that has not yet invaded the breast tissue. These in situ cancer cells grow inside of the pre-exisiting normal lobules or ducts. In situ carcinoma has significant potential to become invasive cancer, and that is why it must be adequately treated to prevent the patient from developing invasive cancer. Invasive cancers have cancer cells that infiltrate outside of the normal breast lobules and ducts to grow into the breast connective tissue. Invasive carcinomas have the potential to spread to other sites of the body, such as lymph nodes or other organs, in the form of metastases.

Approximately 80% of breast carcinomas are invasive ductal carcinoma, followed by invasive lobular carcinomas which account for approximately 10-15% of cases. Invasive ductal carcinomas and invasive lobular carcinomas have distinct pathologic features. Specifically, lobular carcinomas grow as single cells arranged individually, in single file, or in sheets, and they have different molecular and genetic aberrations that distinguish them from ductal carcinomas. Ductal and lobular carcinomas may have different prognoses and treatment options, depending upon all of the other features of the particular cancer.

The remaining cases of invasive carcinoma are comprised of other special types of breast cancer that are characterized by unique pathologic findings. These special types include colloid (mucinous), medullary, micropapillary, papillary, and tubular. It is important to distinguish between these various subtypes, because they can have different prognoses and treatment implications.

Breast Cancer in Men and Children/Adolescents

Breast cancer can also occur in men and children/adolescents. Breast carcinoma in males accounts for less that 1% of all breast cancer cases, and the cancers may be either invasive or in situ. The breast cancers in men can look identical to those seen in women, and most cases consist of invasive ductal carcinoma with positive estrogen receptor (ER) expression. However, the most common breast lesion in males is not breast cancer but is rather gynecomastia, or breast enlargement, which may either involve one breast (unilateral) or both breasts (bilateral).

Breast lesions in children and adolescents are also uncommon and include benign lesions, such as juvenile fibroadenoma, as well as malignant lesions, such as secretory carcinoma. In these pediatric patients, metastatic tumors to the breast, such as lymphoma or alveolar rhabdomyosarcoma, are more common than primary breast cancers.