Guided by genome-wide transcriptomics data [22] in colorectal cancer cells exposed to single (2–10 Gy) or multifractionated of a 2 Gy dose of X-ray ionizing irradiation every 24 h for 5 days (Fig. 1A), we selected four PARP genes including PARP9, PARP12, PARP13 and PARP14 and implemented a more detail analysis of selected gene expression levels in non-irradiated cancer and non-cancerous cell lines and cells subjected to multifractionated 5 × 2 Gy irradiation (Fig. 1B). This evidence concerns the gene PARP9 and colorectal cancer.