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. Here, XBP1 is linked to breast cancer.