How does breast cancer develop

Initially, carcinoma cells are confined within the lobule and adjacent ducts. These are known as non-invasive cancers or 'carcinoma in situ'. As with invasive disease, there are two main types - ductal carcinoma in situ (DCIS) and lobular carcinoma in situ (LCIS). Under the microscope these look different and, clinically, these two types of non-invasive cancer behave differently and require different treatments. Certain types of DCIS develop characteristic tiny particles of calcium within them. These particles show up as tiny white dots on a mammogram. DCIS is much more common than LCIS. DCIS accounts for over one fifth of all types of cancer detected by breast screening. DCIS is treated by surgery which may be followed by radiotherapy and hormonal treatment. LCIS when diagnosed is usually treated by simple follow up with regular mammograms or with hormonal tablets (tamoxifen). Only rarely is surgery used for LCIS. DCIS is considered to be a pre-malignant breast disease. It is not early breast cancer, but if left untreated DCIS cells eventually spread into the surrounding connective tissue of the breast to form an invasive cancer. The time period in which DCIS changes into an invasive cancer appears to be over months and years rather than days or weeks. When an invasive cancer has developed, it is at this stage that there is a risk that cancer cells can spread to nearby lymph glands, the most common lymph glands affected being in the axillary (armpit) region. Cancer cells can also enter the blood stream through the blood vessels that supply the cancer and then move to other organs of the body where they grow and cause problems in these organs. The most common sites for breast cancer to spread to are the bones, lungs, liver and brain. Sarcomas if they spread do so mainly through the bloodstream.