Early breast cancer is subdivided into 2 major categories: in situ disease (mainly in the form of ductal carcinoma in situ), and invasive cancer. Both are heterogeneous processes with very variable appearances, biology and clinical behaviour (see the early and locally advanced breast cancer full guideline for more information).
Invasive breast cancer is the most common type of cancer in the UK and is by far the most common cancer among women. Cancer Research UK reported that 49,961 people were diagnosed with invasive breast cancer in the UK in 2010, more than 99% of whom were women. In the same year, 5765 women in the UK were diagnosed with in situ breast cancer.
Metastatic breast cancer is an advanced stage of the disease when it has spread to other organs. An estimated 5% of people with newly diagnosed breast cancer have metastatic breast cancer, and approximately 30% of people with newly diagnosed localised breast cancer will later develop metastatic breast cancer. Common sites of metastasis include bone, liver, lung and brain (see the NICE technology appraisal on lapatinib and trastuzumab).
Various prognostic factors are considered when planning the management of breast cancer. Tumours that overexpress the human epidermal growth factor receptor 2 (HER2) protein grow and divide more quickly, so women with HER2-positive tumours generally have a worse prognosis than women with HER2-negative tumours (see the NICE technology appraisal on lapatinib and trastuzumab). HER2 positivity is seen in approximately 15% of early invasive breast cancer (see the early and locally advanced breast cancer full guideline).