DDR2 and squamous cell carcinoma: In addition to the essential roles of the wild type of DDR in cancer pathology and prognosis, various mutations of DDR1 and/or DDR2 have also been reported in numerous types of cancer cells, for instance, G1486T(DDR1) and A496S(DDR1) in lung cancer [44], N502S(DDR1), A533S(DDR1), and A803V(DDR1) in acute myeloid leukemia (AML) [79,80], and S768R(DDR2) in squamous cell carcinoma [81].