HOXB13 protein expression in metastatic lesions is a promising marker for prostate origin.

The HOXB13 gene is a member of the homeobox gene family, and prostate development depends on HOXB13 function. HOXB13 is a very sensitive and specific marker of prostate tissue and prostate cancer. When the origin of a tumor in a resection specimen or in biopsy material is unclear, it allows determining the prostate as the primary. Our aim was to determine whether HOXB13 has similar sensitivity for determining prostate origin of lymph node and bone metastases. We retrieved cases of lymph node and bone metastases of histologically confirmed prostate cancer (PCa) and selected lymph node metastases of urothelial carcinoma (UCa). A panel of antibodies against HOXB13, PSA, ERG, Androgen receptors, p504S, p63, GATA-3, CK7, and Uroplakin 2 and 3 was tested on these tissue samples. Two pathologists analysed and scored staining as either 0 (negative) or + (positive). The selected cohort consisted of 74 cases of lymph node and 15 of bone metastases of PCa and 15 of lymph node metastases of UCa. HOXB13 was expressed in 93 % of lymph node and in 33 % of bone metastases of PCa. All lymph node metastases of UCa were negative. Sensitivity of HOXB13 as a marker for prostate origin in lymph node metastases was 93 % and for bone metastases 33 %. Inter-observer variability in assessment of staining was good, as only two (1.9 %) of lymph node metastasis of PCa were discordant. HOXB13 is a useful marker for prostate origin when doubt exists regarding the site of the primary of a metastatic lesion. On bone metastases, HOXB13 immunohistochemistry performed less well, probably due to the use of tissue decalcification.