Shares of Xencor fell as much as 16% on Wednesday after the company reported what investors saw as lacklustre efficacy results from a Phase II trial of its XmAb bispecific antibody vudalimab, which targets immune checkpoint receptors PD-1 and CTLA-4.
Analysts at BMO Capital Markets said the study evaluating vudalimab monotherapy in 14 high-risk metastatic castration-resistant prostate cancer (mCRPC) patients was nevertheless "encouraging" on efficacy given the heavily-pretreated population. The cohort underwent a median four prior lines of therapy, most of whom had received chemotherapy, while 29% had received prior therapy with Novartis' radioligand therapy Pluvicto (lutetium Lu 177 vipivotide tetraxetan).
Out of 12 evaluable patients, Xencor said vudalimab achieved an objective response rate (ORR) of 33% (4/12), but with only three confirmed partial responses. A quarter of evaluable patients showed PSA marker reductions exceeding 90% from their baseline levels (PSA90).
While investors appeared underwhelmed, BMO analysts noted that these results stack up favourably against competing treatments where ORRs have ranged from roughly 11% to 26% and PSA90 rates have hovered around 10% to 26%.