I want to recommend a recently published book by Dr. Jules Berman titled Neoplasms: Principles of Development and Diversity. This book defies easy categorization. In one sense it is a textbook. But it is so much more! Basically, it sets forth basic principles to account for the overwhelming diversity of human neoplasia that "can serve as a baseline set of ideas that can be improved or disproved by the readers." I guarantee that your assumptions about cancer and tumor biology will be challenged. This is a book I've been waiting for my whole career. As one fortunate enough to have had an undergraduate medical course in embryology, I have always been impressed by the similarities between embryological development and neoplasia. This book approaches neoplasia from this perspective. Parenthetically, the new edition of Gray's Anatomy has a lovely chapter on embryogenesis that you might want to read along with this book (as a refresher!). Another book worth considering along these lines is the flipside of Neoplasms called (provocatively) Mutants (On the Forms, Varieties and Errors of the Human Body) which looks at diversity in terms of development. If you are wondering, I have no connections, financial or otherwise, to any of these books or authors, although I have emailed Dr. Berman about the possibility of using his book to teach medical students.