Very understandably, 'nothing more to be done' is a phrase that is very upsetting to hear. But it doesn't mean the end of care and support for your father. What it does mean is that his specialist doesn't think there is any treatment left that has a reasonable chance of controlling or reducing the leukaemia.
This decision will change the emphasis of your father's medical management from 'active treatment' to 'supportive care'. The emphasis will be on ensuring your father is comfortable and maintaining his quality of life whilst providing practical and emotional support to him and the family.
There is often a sense of desperation when people hear the specialist say there is nothing more that can be done. So your question is one that is frequently asked. Very often, though, it is asked by relatives and not by the person who has the leukaemia. Sometimes this is because the person who is ill has already come to terms with their condition, has accepted their situation and may even be relieved not to have to undergo further treatment. But, their relatives, may feel it is important not to 'give up' and that 'something must be done'. So, first of all talk to your father to make sure that he wants to look for further active treatment. If he is sure this is what he wants to do there are options open to him.
The first is for your father to talk to his specialist. He can ask about experimental treatments and clinical trials. His specialist may say there is nothing suitable or he may know of experimental treatments which are being tested at another hospital and might offer to refer your father there for advice.
Your father can also ask his consultant or GP to arrange a further opinion from a consultant at another hospital. The new specialist may offer the choice of further treatment or they may agree that further treatment wouldn't be helpful. But at least your father will know that he has explored every option open to him.
If he is offered an experimental treatment the chances that your father will get a benefit from it are likely to be small. But, for some people having active treatment helps them to feel positive and hopeful despite knowing the chances of benefit are not high. The disadvantages of this type of treatment may be the disruption, and possible side-effects it brings.
