Waiting for biopsy results…..rapid weight loss

Hi there, we're currently waiting for the results of a biopsy for my Dad who had a possible recurrence of colon cancer. CT scan shows no spread but he hasn't eaten in 2 months and has lost 3 stone and looks so awful. He's started taking ENSURE. The changes in him are frightening and I feel so helpless. Has anyone else had this speed of weight loss and what did you do? He's waiting to see a dietician but it's a long waiting list.