PPP1R1B and breast carcinoma: However, another study indicated that t-DARPP, but not DARPP-32, was overexpressed in a trastuzumab-resistant breast cancer cells, and demonstrated that t-DARPP overexpression was sufficient to confer resistance to trastuzumab and suppress trastuzumab-mediated dephosphorylation of AKT in sensitive breast cancer cells [42].