Many chemotherapeutic agents compromise the integrity of the mucosal barrier in the gut, allowing translocation of gram-positive bacteria in secondary lymphoid organs. While this has, until recently, been considered an undesirable side-effect, it may also represent one mechanism by which chemotherapy stimulates an effective anti-cancer immune response. The purpose of this research is to test whether bacteria that normally live in the intestines play a role in fighting cancer. It is believed that the development and behavior of these immune cells may be influenced by bacteria and other microorganisms living in the gut. In turn, the activities of these immune cells could work with anti-cancer therapies to make them more, or less, effective. The hypothesis is that gut microbial composition can influence immune response to the tumor, resulting in inter-individual differences in the response to anti-cancer therapies.