Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other investigational agents; patients may not be receiving any other treatment for their rectal cancer during study participation and within 30 days prior to study treatment Participants may not be receiving any other study agents concurrently with the study drugs Participants may not be receiving any other research study agents Participants may not be receiving any other study agents for at least 7 days prior to enrollment Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants who are currently receiving other anticancer agents. Participants may not be receiving any other study agents Participants may not be receiving any other study agents, and may not have received any other investigational agents within 6 months prior to study entry Patients receiving any other study agents Participants who are receiving any other study or off protocol anti-cancer agents May not be receiving any other study agents Participants may not be receiving any other study agents PHASE I: Participants may not be receiving any other study agents within 2 weeks of initiating treatment Participants may not be receiving any other study agents concurrently with the study drugs Participants receiving any other study agents Participants may not be currently receiving any other experimental agents Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other study agents. Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other study agents Participants may not be receiving any other study agent Participants may not be receiving any other study agents Participants may not be receiving any other study agents during the study or within 4 weeks of the start of the trial EXPANSION COHORT ONLY: Participants may not be receiving any other study agents during the study or within 4 weeks of the start of the study Participants may not be receiving any other study agents Participants may not be receiving any other study agents at the time of first treatment Participants may not be receiving any other study agents Participants may not be receiving any other study agents or other types of cancer therapy while on this protocol except for disease progression Participants may not be receiving any other study agents within 21 days prior to entry on the study Participants may not be receiving any other study agents Patients receiving any other study agents Participants who are receiving any other investigational agents that might interact with study medication or influence the measurement of study outcomes Patients receiving any other study agents