For a patient with terminal ileal Crohns disease who requires chemoRT for distal rectal cancer, can mercaptopurine (6MP) be continued during that phase of treatment?  

6MP is an antimetabolite that was not developed as a radiosensitizer. So at the right dose it is probably a selective radiosensitizer similar to 5FU. There are no data reported with radiation and 6MP, so this statement is just deductive reasoning. The worst that can happen is an enhancement of acute...