CTNNB1 and melanoma: Since activation of the Wnt/β-catenin pathway has also been demonstrated to cause T cell exclusion32, CTNNB1 mutations may also contribute to the relatively poorer responses to immunotherapy observed in some advanced stage mucosal melanoma patients33,34 Hotspot mutations were also identified in the oncogenes MAP2K1 and KRAS, which together with a BRAF fusion, further highlight the reliance on MAPK pathway activation in this tumor type.