KIAA1549 and pilocytic astrocytoma: We measured the MSSs in a panel of pLGG cell lines45,46 (n = 5) comprising pilocytic astrocytoma (PA) cell lines harboring a KIAA1549:BRAF fusion (DKFZ-BT66, DKFZ-BT308, DKFZ-BT317), a PA and a pleomorphic xanthoastrocytoma (PXA) cell line harboring a BRAF V600E mutation (DKFZ-BT314 and BT40, respectively), melanoma cell lines (n = 55) with BRAF mutations and known high MAPK pathway activity36 (from GSE7127; used as positive control), and multiple myeloid cell lines (n = 11) with MAPK wild-type and known low MAPK pathway activity36 (from GSE6205; used as negative control).