Chemotherapy is used to treat cancerous cells with the use of anticancer drugs. Most chemotherapy drugs work by interfering with cell reproduction. All cells go through five phases – one resting phase (how cells spend most of their lives), three phases leading up to reproduction, and the final phase (called mitosis) when the cell actually divides into two new cells. Most chemotherapy drugs do not affect cells that are in the resting phase but, depending on the type of drug, they do attack cells in one or more of the reproduction phases. The drugs cannot distinguish cancer cells from normal cells and can affect normal cells undergoing reproduction phases. Oncologists work to find the best combination of drugs, given in specific intervals, in order to target the most cancer cells while avoiding damage to normal cells. Some types of cancer can be treated with chemotherapy alone while others may need a combination of treatments such as radiation therapy and surgery. Because chemotherapy drugs can affect more than just cancer cells, there can be many side effects during treatment. To help patients tolerate their treatment, many drugs and therapy techniques have been developed to ease the side effects from chemotherapy.