This book would combine chapters written by the most qualified authors around the world whose research encompasses the effect of morphine or other opioids on tumor growth and metastasis. This includes clinicians involved in trials determining which type of post surgical pain management can minimize the risk of recurrence or metastasis, researchers working on animal models and studying the effect of morphine on tumors, and most importantly the mechanism for this effect, and lastly cell biologists. There is currently a lot of research going on trying to reconcile the pro- and anti-cancer aspects of opioids actions.