Biology question about drug used for chemotherapy?

5-Fluoro-uracil (5-FU) is a drug commonly used in chemotherapy treatment of cancer. Cancer cells are usually very fast growing cells; other cells in your body, which are also fast growing, are bone marrow cells (which produce red and white blood cells) and hair follicle cells (which produce hair). Suggest why 5-FU can be a good treatment for cancer. Also, describe why 5-FU has side effects of low blood counts and hair loss.