DDR1 and neoplasm: The tumor specimens were then subjected to immunohistochemical staining to analyze the expression of DDR proteins, and our data showed that the expression level of P-CHK2 was mildly increased in tumors derived from HBX-expressing cells compared with those derived from control cells, whereas the increase extent of P-CHK1 was not affected by HBX overexpression (Figs. 5d, e).