Cells divide in order to create new cells. Mitosis is the process required to create a new cell. A cell that is about to divide is called a mitotic figure. Pathologists can see mitotic figures when they look at a tissue sample under the microscope. Mitotic figures are easy to see because the genetic material inside the nucleus changes colour and shape before the cell divides.
The process of mitosis is divided into stages (see picture below). These stages are called prophase, metaphase, anaphase, and telophase. During prophase, the amount of genetic material in the cell doubles so that there will be enough for two new cells. During metaphase the genetic material lines up in the centre of the cell. During anaphase, the cells begin to split into two cells and the genetic material is divided with half going to each new cell. Finally, in telophase, two new cells are formed with their genetic material inside the nucleus.
Dividing cells are found in both normal tissues and in abnormal tissues such as cancers. Because cancers grow a lot faster than normal tissues, they often have many more dividing cells. Mitoses are also present in many reactive (non-cancerous) conditions. A tumour that has many mitoses is growing quickly, but this may also mean it is more susceptible to treatments such as chemotherapy which targets cells that are dividing.