MAPK3 and neoplasm: The samples with the heterogenous expression of CK15, exhibiting CK15-negative tumor regions (Figure 3, inset b, white arrow) in the vicinity of cells with marked CK15 expression (Figure 3, inset b, black arrow), showed a similar pattern of staining of P-Erk1/2 (Figure 3, inset c, white and black arrows, respectively).