DDR1 and melanoma: Immunohistochemical analysis of DDR1 and DDR2 expression in benign nevi and malignant primary and metastatic melanocytic skin lesions further showed that DDR1 and DDR2 levels significantly increased during melanoma progression, indicating that DDR1 and DDR2 may represent novel prognostic factors for melanoma (Fig 3B; Appendix Fig S3).