The emerging role of XBP1 in cancer

X-box binding protein 1 (XBP1) is a unique basic-region leucine zipper (bZIP) transcription factor whose dynamic form is controlled by an alternative splicing response upon disturbance of homeostasis in the endoplasmic reticulum (ER) and activation of the unfolded protein response (UPR). XBP1 was first distinguished as a key regulator of major histocompatibility complex (MHC) class II gene expression in B cells. XBP1 communicates with the foremost conserved signalling component of the UPR and is essential for cell fate determination in response to ER stress (ERS). Here, we review recent advances in our understanding of this multifaceted translation component in cancer. In this review, we briefly discuss the role of XBP1 mediators in the UPR and the transcriptional function of XBP1. In addition, we describe how XBP1 operates as a key factor in tumour progression and metastasis. We mainly review XBP1's expression, function and prognostic value in research on solid tumours. Finally, we discuss multiple approaches, especially those involving XBP1, that overcome the immunosuppressive effect of the UPR in cancer that could potentially be useful as antitumour therapies.