HOXB13 is a protein that in humans is encoded by the HOXB13 gene.This gene encodes a transcription factor that belongs to the homeobox gene family. HOXB13 expression can identify patients with limited benefit of endocrine treatment. This has been shown for gene expression, as well as protein levels.

        The HOXB13: IL17BR ratio has been identified to predict clinical outcome in the setting of adjuvant tamoxifen monotherapy of breast cancer as well as tumor aggressiveness. Further studies have shown that HOXB13 in particular can indicate benefit or not from prolonged tamoxifen treatment. Patients with high-expressing HOXB13 tumors did not benefit from prolonged treatment, suggesting that HOXB13 is involved in tamoxifen resistance. Tamoxifen-treated patients with estrogen receptor-positive tumors expressing none or low levels of HOXB13 had a clear benefit from tamoxifen in terms of longer distant recurrence-free survival.