SOX9 and cancer: However, the fact that we found gain of the mutant SOX9 allele as well as overexpression of the mutant allele in the absence of the WT allele argues that truncated SOX9 may serve as an oncogene in CRC, or as a gain of function tumor suppressor gene as well described in the case of TP53. However, data across the Cancer Genome Atlas (TCGA) show that SOX9 is altered in a pattern typically seen in oncogenes: it is mutated and amplified in multiple cancer types, and rarely is the whole gene deleted [11].