If you have finished treatment for ovarian cancer and are in remission, there is little to stop you going for as long as you want. If you are having chemo, you may need to time it with your treatment cycles. Or travel within the UK and have treatment pre-arranged at local clinics. You could go on a world cruise, but remember the NHS will only give you three months of medication. If you are going for longer than three months you may have to get more privately or arrange a special licence with the Home Office if you need to take large quantities of controlled drugs e.g. morphine.