I have pancreatic adenocarcinoma and for the majority of my adult life was misdx'd as being diabetic (non-diabetic after Whipple, which is just the opposite of most) so I stayed away from any sugars/sweets, etc for quite some years and still developed cancer. Although it's always better to maintain a healthy diet, unless there are some diabetic issues or food processing issues, sugars from fruits should not be a major concern.
My prayers are with your family.