Animal models of cancer pain

Modern cancer therapies have significantly increased patient survival rates in both human and veterinary medicine. Since cancer patients live longer they now face new challenges resulting from severe, chronic tumor-induced pain. Unrelieved cancer pain significantly decreases the quality of life of such patients; thus the goal of pain management is to not only to alleviate pain, but also to maintain the patient's physiological and psychological well-being. The major impediment for developing new treatments for cancer pain has been our limited knowledge of the basic mechanisms that drive cancer pain and the lack of adequate animal cancer pain models to study the molecular, biochemical and neurobiological pathways that generate and maintain cancer pain. However this situation has recently changed with the recent development of several novel animal models of cancer pain. This review will focus on describing these animal models, many of them in rodents, and reviewing some of the recent information gained from the use of these models to investigate the basic mechanims that underlie the development and maintenance of cancer pain. Animal models of cancer pain can be divided into the following five categories: bone cancer pain models, non-bone cancer pain models, cancer invasion pain models, cancer chemotherapeutic-induced peripheral neuropathy models, and spontaneous occurring cancer pain models. These models will be important not only for enhancing our knowledge of how cancer pain is generated, but more importantly for the development of novel therapeutic regimes to treat cancer pain in both domestic animals and humans.