RUNX1 and neoplasm: Despite the reported scarcity of RUNX1 mutations (≤5% in three large independent studies18, 19, 20), RUNX1 was undetectable in 12 of the 31 ER+ ductal invasive carcinomas, indicating that its function may be lost, at least transiently, in far more than the ≤5% of tumours with RUNX1 mutations (Supplementary Table 1).