JAK1 and melanoma: JAK1/2 mutations may, however, not be as frequent as HLA/B2M alterations, as a screening for JAK1/2 mutations in two unselected cohorts only found 1/23 (4%) malignant melanoma with a JAK2 mutation and 1/16 (6%) mismatch repair deficient metastatic colon cancers with a JAK1 mutation, although both were identified in non-responders [55].