In summary, our study highlights significant differences in HER2 expression patterns between metastatic prostate cancer and urothelial carcinoma, with low and heterogeneous expression in prostate cancer limiting the general applicability of HER2-targeted therapies, whereas the higher and more consistent expression in urothelial carcinoma supports its potential role as a therapeutic target although still in selected cases. This evidence concerns the gene ERBB2 and Familial prostate cancer.