MKI67 and melanoma: In addition, MEKi alone was capable of reducing tumour mass more efficiently than C + T. Finally, when excised tumours were stained for the commonly used proliferation marker Ki67, there were significantly reduced numbers of Ki67-positive cells in the groups treated with trametinib (MEKi) alone or in combination with C + T (Figure 6D), whereas the expression of the commonly used immunohistochemistry melanoma marker S100 [36] remained stable across all groups (Figure S4E).