The previously described study (Hoskins et al, 2008) genotyped 107 metastatic CRC patients treated with irinotecan regimens for single-nucleotide polymorphisms (SNP) in Top 1, CDC45L, NFKB1, PARP1, TDP1 and XRCC1. These SNPs were tested for association with the most frequent and significant side effects of irinotecan, namely grade three out of four diarrhoea and neutropenia. The gene discussed is TDP1; the disease is Decreased total neutrophil count.