Breast Cancer Classification

Classification

Main article: Breast cancer classification

Breast cancers can be classified by different schemata. Every aspect influences treatment response and prognosis. Description of a breast cancer would optimally include multiple classification aspects, as well as other findings, such as signs found on physical exam. Classification aspects include stage (TNM), pathology, grade, receptor status, and the presence or absence of genes as determined by DNA testing:

• Stage. The TNM classification for breast cancer is based on the size of the tumor (T), whether or not the tumor has spread to the lymph nodes (N) in the armpits, and whether the tumor has metastasized (M) (i.e. spread to a more distant part of the body). Larger size, nodal spread, and metastasis have a larger stage number and a worse prognosis.
  The main stages are:
  Stage 0 is a pre-malignant disease or marker (sometimes called DCIS: Ductal Carcinoma in Situ) .
  Stages 1–3 are defined as 'early' cancer and potentially curable.
  Stage 4 is defined as 'advanced' and/or 'metastatic' cancer and incurable.

• Histopathology. Breast cancer is usually, but not always, primarily classified by its histological appearance. Most breast cancers are' derived from the epithelium lining the ducts or lobules, and are classified as mammary ductal carcinoma. Carcinoma in situ is proliferation of cancer cells within the epithelial tissue without invasion of the surrounding tissue. In contrast, invasive carcinoma invades the surrounding tissue.^[11]

• Grade (Bloom-Richardson grade). When cells become differentiated, they take different shapes and forms to function as part of an organ. Cancerous cells lose that differentiation. In cancer grading, tumor cells are generally classified as well differentiated (low grade), moderately differentiated (intermediate grade), and poorly differentiated (high grade). Poorly differentiated cancers have a worse prognosis.

• Receptor status. Cells have receptors on their surface and in their cytoplasm and nucleus. Chemical messengers such as hormones bind to receptors, and this causes changes in the cell. Breast cancer cells may or may not have three important receptors: estrogen receptor (ER), progesterone receptor (PR), and HER2/neu. Cells with none of these receptors are called basal-like or triple negative. ER+ cancer cells depend on estrogen for their growth, so they can be treated with drugs to block estrogen effects (e.g. tamoxifen), and generally have a better prognosis.
  Generally, HER2+ had a worse prognosis,^[12] however HER2+ cancer cells respond to drugs such as the monoclonal antibody, trastuzumab, (in combination with conventional chemotherapy) and this has improved the prognosis significantly.^[13]

• DNA microarrays have compared normal cells to breast cancer cells and found differences in hundreds of genes, but the significance of most of those differences is unknown.