MAPK1 and neoplasm: Importantly, clear signal for phospho-ERK1/2 was observed in the detaching tumor cells (Fig 7C, arrows) and the isolated tumor cells (Fig 7C, arrowheads), indicating that ERK is activated in the disseminating tumor cells, in which mesenchymal phenotypes such as loss of E-cadherin expression and loss of cell polarity are acquired (Fig. 7B).