Cabibi et al. have demonstrated that such drug resistance may be due to a low proliferative activity of tumor cells, as the analysis of 15 SRCC samples showed very low levels of Ki-67 expression (a proliferation marker) and weak positivity for thymidylate synthase (key enzyme for DNA synthesis pathways targeted by 5-FU)13,23,24. The gene discussed is MKI67; the disease is neoplasm.