Hi - have you read the info about clinical trials on Cancer Research?

www.cancerresearchuk.org/.../find-a-clinical-trial

I found the multiple links on this page really helpful. Hopefully, it will answer some of your queries and signpost you where you need to go. There is also some info about eligibility for trials in the "How to Join a clinical trial" section. Sometimes people are, sadly, not deemed eligible for trials. 

It sounds like a really tough situation with your mum not eating and she may not be considered strong enough to participate in a trial. This can be a hard thing to accept. I feel you really need to know you have explored every option and hope the link is able to answer some of your queries.