On identifying MYC repression as a possible biomarker of HDAC inhibitor activity from the strategy of analyzing, firstly, PRAVO study patients' PBMC, and secondly, vorinostat-treated colorectal carcinoma xenografts, and additionally recognizing this drug as a rational approach for biological optimization of radiation effect in pelvic gastrointestinal carcinoma [10], we investigated whether MYC might be expressed in the target tissue of a well-established pelvic radiotherapy protocol. This evidence concerns the gene HDAC9 and colorectal carcinoma.