A very small and insightful book by a Zen monk that I found so encouraging is "True Love" by Thich Nhat Hanh (pronounced "tick not hon"). It's not about cancer, but can be so useful to caregivers when the loved ones they are caring for are in emotional pain. Some of the chapters describe "being there when someone is suffering", "deep listening", "restoring peace within yourself". It's a very quick read book and one that allows picking a chapter here and there without having to read every short chapter in specific order.