Histone H1.5, a novel prostatic cancer marker: an immunohistochemical study.

Histone H1.5 (HH1.5) is a somatic subtype of the histone H1 family of linker proteins that are located in the nucleus and play a role in stabilizing higher-order chromatin structure, gene expression, DNA repair, and cell proliferation. Recently, differential immunohistochemical expression of HH1.5 has been found in various neuroendocrine neoplasms. This study aimed to investigate the immunohistochemical expression of HH1.5 in prostatic adenocarcinomas. Sixty-three prostate needle core biopsies, 9 radical prostatectomy specimens, and 3 metastatic prostate cancer cases were evaluated. HH1.5 immunohistochemistry revealed strong nuclear reactivity in 68 (93%) of 73 cases of prostate adenocarcinomas, compared to only 7 (9%) of 75 cases of benign prostatic glands (P ≤ .0001). In all positive benign prostate epithelium, HH1.5 was limited to focal and weak reactivity. Similarly, all 23 foci of high-grade prostatic intraepithelial neoplasia exhibited focal staining, with the vast majority having only weak nuclear reactivity. Increased HH1.5 reactivity was observed in Gleason patterns 4 and 5 as compared to Gleason pattern 3, 72% and 56%, respectively (P ≤ .02). All 3 metastatic prostate cancer cases showed strong nuclear reactivity. HH1.5 may be a useful diagnostic tool in evaluating prostatic biopsies, particularly with small foci of cancer. Further studies are needed to support these findings and investigate the possible prognostic significance of HH1.5 in prostatic adenocarcinomas.