ERBB2 and breast cancer: Despite the fact that mUC has one of the highest rates of HER2 expression of any solid tumor (12.4% in urothelial carcinoma, 11.3% in esophagueal and esophagogastric junction cancers and 10.5% in breast cancer) [43], clinical trials analyzing HER2 targeting in those patients have not shown a clinically significant benefit.