SKP1 and rectal cancer: Linking the 26S proteasome/ubiquitin system to radiation sensitivity, a decreased expression of components of this pathway was congruently associated with a more radioresistant phenotype in breast, laryngeal, lung, esophageal and rectal cancer and/or cancer cell lines [105,106,107,108,109,110], which is in line with the observation of enhanced expression of ubiquitin and SKP1 in the radiosensitive HPV-positive OPSCC population.