Furthermore, our PCA performed with the TCGA cohort, based on expression data from different gene sets (all deregulated genes or subsets of genes from the Qiagen PCR Arrays) did not allow discriminating colon vs. rectal tumors or CRC samples according to APC or KRAS mutational status (Fig. 2, Additional file 4). The gene discussed is KRAS; the disease is colorectal carcinoma.