Although XBP1 and XBP1s share extensive sequence homology, XBP1s acquires unique C‐terminal transcriptional domains, which enable it to function as a potent transcription factor and a critical effector of the IRE1α–XBP1 pathway.[9] Thus, we designed junction‐targeting primers for XBP1s to quantify via qRT‐PCR and assessed the expression levels of XBP1 and XBP1s in early breast cancer tissues. This evidence concerns the gene ERN1 and breast carcinoma.