Immunostaining of the androgen receptor and sequence analysis of its DNA-binding domain in canine prostate cancer

Prostate cancer in the dog (cPC) has many features in common with hormone refractory human prostate cancer. As cPC is seen more often in castrated dogs, the contribution of the androgen receptor (AR) to the development of prostate cancer remains questionable. The aim of the present study was to evaluate the presence of the AR by immunohistochemistry in cPC. AR staining was observed in most tumors from intact and castrated dogs, but the proportion of positive cells and the staining intensity were much lower than in the prostate of healthy, non-castrated dogs. Most of the positive staining was seen in the cytoplasm rather than in the nuclei of the tumor cells. The predominant cytoplasmic localization was not related to mutations in exon 3 of the DNA-binding domain of the AR, as shown by sequence analysis of microdissected AR positive tumor cells. Other mechanisms that lead to an impaired androgen-AR signaling or a basal/stem cell like origin may explain the low cytoplasmic AR staining in cPC.