ERBB2 and neoplasm: Investigative efforts in a HER2+ human breast carcinoma (BT-474) xenograft in rats have shed light on responder/nonresponder dichotomies in this therapeutic context, finding that trastuzumab delivery with FUS BBB/BTB-O reduced tumor outgrowth in some (4 out of 10) rats but conferred only a mild response in others (6 out of 10) (64).