Sudden loss of appetite

Hi,

Please bear with me as I am new to this support network.

My dad is a retired GP who was working as a very health medical consultant until the age of 73.  He is currently 75 and was in April this year  diagnosed with stage 4 cancer of the gall bladder with secondary liver metastsis. Two thirds of his gall bladder are impacted as are some lymph nodes and the liver has approx 7 scattered spots less than 2cm each.  It was a shock to the whole family as he was very healthy to look at and had no symtpoms.  He just went to see the GP as he was feeling bloated and was burping a lot. His first biopsy showed no cancer, only dead scar tissue.  His second biopsy and PET scan confirmed it was cancer.  He started his chemothrapy almost immediately and has now completed 6 cycles of Cisplatin/Gemcitabine.  Genetic molecular test also completed but to no avail. He had a break from treatment after the 3rd cycle he was found to have delerium - confusion with memory loss.  After a break of 3 weeks he had 2 more cycles and then unfortunately fell and fractured his spine which also resulted in treatment being paused for a further 2 weeks and a 9 day hospitalisation where he was kept in isolation due to his immune system beign weak.  This do not help his mental state at all and the deleruim and confusion are more prominent.  He had his last chemo 2 weeks ago and we are awating a PET scan to see how effective the 6 cycles have been and to decide next steps.  All through the chemo he has coped well physically, no feeling ill, no pain, great appetite as it was pre cancer.  Only issues have been the confusion and excess fluid causing swollen ankles and recently constipation. 8 days ago he went from eating very well to barely eating at all.  I would say 80% less.  He's losing around a kilo a day.  We consitently remind him of the importance of eating using the science we have heard him, as a doctor, use so many times before with elderly relatives.  It works and he eats a little with some persuasion.  We have adopted the little and often approach and quized him about the reasons why is not wanting to eat - he says he wants to eat but doesn't know why he is not.    We are so worried at the weight loss and sudden loss of appetite.  Has anyone experienced this before and did you find any solutions please?  Thank you.