There are numerous ways breast cancer is classified. Like most cancers, breast cancer can be divided into groups based on the tissue of origin, e.g. epithelial (carcinoma) versus stromal (sarcoma).

The vast majority of breast cancers arise from epithelial tissue, i.e. they are carcinomas, which can be divided further into subclassifications (e.g. DCIS versus LCIS versus papillary carcinoma).

• Location of the tumour origin - breast duct (i.e. ductal) versus breast lobule (i.e. lobular).

• Histology .

• Grade of tumour - well-differentiated (looks almost like normal tissue) versus poorly differentiated (does not look like any normal tissue/mass of proliferating cells) versus moderately differentiated (somewhere between poorly differentiated and well-differentiated).

• Stage of the tumour.Immunohistochemical marker status - (ER positive versus ER negative versus HER2/neu positive versus HER2/neu negative), e.g. triple negative breast cancer which is ER negative, PR negative and HER2/neu negative.

• TNM classification - Tumour size/invasiveness - presence of invasion (poorer prognosis) versus in situ (better prognosis). Nodal status - Presence/absence of metastases.

• •