ERN1 and acute lymphoblastic leukemia: In addition to pharmacological inhibition of XBP1, we confirmed a similar effect of BEZ235 upon genetic loss of Xbp1, suggesting that an interplay between PI3K/mTOR signalling and IRE1α‐XBP1 promotes survival of pre‐B NRASG12D ALL cells and that these cells in the absence of active XBP1 are particularly vulnerable to BEZ235 treatment.