<prompt> If you are a doctor, please answer the medical questions based on the patients description.I need information about the chemo drug 5-FU. It is not listed on your list of drugs but is listed in treatment for stage IV rectal cancer. This cancer has metastisized to liver - 5 lesions - and lungs - 2 lesions on 1 lobe; 1 leison on other lobe. I want to know its side effects. Chemo starts tomorrow for 5 days a week for 4 or 5 weeks with 5-FU and also leucovorin. Simultaneously, radiation therapy will take place 5 days a week for 4-5 weeks.  <response>: Hi, I have gone through your query. Since the rectal cancer has spread to liver, only chemotherapy and radiotherapy will be done.5-FU Fluorouracil is mixed with leucovorin in order to increase 5-FU activity. Most common side effects of 5-FU includes:DermatitisMyositisDiarrheaMyelosuppression Bone Marrow SuppressionDo consider positive feedback as a credit to my work. Let me know if you have any further questions. You can contact me on my page 