KRT81 and cancer: Furthermore, multiplex immunofluorescence for pancytokeratin (PanCK), MCT4 and KRT81, an established QM marker [19], in 6 PDAC FFPE specimens, showed that the proportion of MCT4-positive cells was higher among KRT81 positive (30–50%) than KRT81-negative cancer cells (< 20%) (Fig. 3d).