The Bloom-Richardson grading system , or the modified Bloom-Richardson-Elston grading system, is a breast cancer staging system that examines the cells and tissue structure of the cancer to determine how aggressive and invasive the cancer is:

• What percent of the tumor makes normal duct structures? In cancer, there is a breakdown of the mechanisms that cells use to attach to each other and communicate with each other, to form tissues such as ducts, so the tissue structures become less orderly.

• How many mitotic figures (dividing cells) can the pathologist see in a microscope field? One of the hallmarks of cancer is that cells divide uncontrollably. The more cells that are dividing, the worse the cancer.

• Are the cell nuclei uniform like normal breast duct epithelial cells, or are they larger, irregular, and darker ( pleomorphic )? In cancer, the mechanisms that control genes and chromosomes in the nucleus break down. Irregular nuclei are a sign that the mechanisms that control cell reproduction are breaking down.

Each of these features is assigned a score ranging from 1 to 3. The scores are then added together for a grade that will range between 3 to 9. This value is then used to grade the tumor as follows :

• 3-5 Grade 1 tumor (well-differentiated). Best prognosis.

• 6-7 Grade 2 tumor (moderately-differentiated). Medium prognosis.

• 8-9 Grade 3 tumor (poorly-differentiated). Worst prognosis.

Lower grade tumors, with a good prognosis, can be treated with less aggressive surgery and medication, and have a better survival rate.

Higher grade tumors must be treated with more aggressive surgery, radiation, and drugs with worse adverse effects, and have a worse survival rate.