The smaller number of patients with a positive Ki-67 index in lymph node metastasis can also contribute to the poor prognosis attributed to the presence of lymph node metastasis [32, 50, 55, 56] in CCR, since most antineoplastic agents target proliferating cells, cells with a low proliferation rate are more resistant to such treatment [53], and this hypothesis was also stated by Cabibi et al. [44], relatively to the subgroup of patients with breast cancer and lower ki-67 index in lymph node metastasis than in primary tumour. This evidence concerns the gene MKI67 and breast cancer.