Immunohistochemical analysis of cellular proliferation. Immunofluorescence images of Ki67 (green) nuclear labelling of cytokeratin (CK, red) positive neoplastic cells in sections of xenografted tumours from an untreated (A) and Erl + Cet treated (B) BALB/c nude mouse. C: bar graph illustrating the effect of the different treatments on the percentage of cycling (Ki67pos) neoplastic cells within the tumour. CTRL: untreated, ERL: erlotinib, CET: cetuximab, COMB: erlotinib + cetuximab. * p < 0.01 vs CTRL.