The On Dogs and Dying: Inspirational Stories From Hospice Hounds (New Directions in the Human-Animal Bond) is a really helpful book on training and therapy techniques that help increase the quality of life for a dog when they are in extremis. This book will aid you in creating a positive and happy environment for your dog and make their last days, weeks or months more comfortable and enjoyable.
This article from the Dog Cancer Blog is very informative with regards to the quality of life for a dog with cancer:
And if you are looking for some information on dealing with grief and loss, there are a number of informative articles on the Dog Cancer Blog that you may find helpful.
We really hope this book helps both you and your dog.