To assess the in vivo antiproliferative properties of IFN-α during treatment, we have monitored Ki-67 (MIB-1) LI in repeated core needle tumour biopsies obtained at baseline and at week 5 of IL-2- and IFN-α-based immunotherapy in patients with mRCC and correlated the findings with objective response and survival. This evidence concerns the gene MKI67 and neoplasm.