CCNE2 and Burkitt lymphoma: Two key cell cycle regulatory genes, CCNE1 and CCNE2, which are implicated in CDK4/6i plus ET resistance [6, 11], as well as E2F1 [2], the key downstream target of RB1, were significantly increased in PD versus BL tumors (Additional file 6: Fig. S9a, 9b) [2].