Early data on OncoMed's cancer antibodies 'intriguing, but preliminary'

Analysts are reserving judgment until data from Phase 2 trials is available.

OncoMed has posted early data on two antibodies for cancer, but investors' eyes are still focused on prospects for its troubled stem cell drug tarextumab.

The first-in-human data on OMP-305B83 (anti-DLL4/VEGF bispecific) and OMP-131R10 (anti-RSPO3) antibodies checked the right boxes—safety profile OK, dose selected for Phase 2 studies—but shares in the company remain weak and were down in after-hours trading yesterday.

Partial responses and stable disease were seen with the bispecific antibody as a monotherapy in around a third of treated advanced ovarian and uterine tumor patients, said the company. Drilling down into the data in the 51-patient study, most of those were stable disease (16 patients) while two showed a partial response. 

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Analysts at Leerink pointed out in a research note that AbbVie's bispecific DLL4/VEGF inhibitor ABT-165 achieved a partial response rate of 25% in a Phase 1 trial reported at this year's ASCO congress.

Meanwhile, the anti-RSPO3 Phase 1a/b trial showed "evidence of target engagement and some encouraging signals of prolonged stable disease," according to OncoMed's chief medical officer Jakob Dupont. Leerink said the data were difficult to interpret, however, for example because "RSPO3 gene expression levels did not seem to correlate with tumor shrinkage in the trial."

Overall, while the scientific rationale for these agents "is very intriguing, early results from both dose-escalation trials look very preliminary" say the analysts, and they are reserving judgment on their potential until data from Phase 2 trials is available in the first half of 2017.

In the meantime, OncoMed's shareholders remain fixated on the prospects for GlaxoSmithKline-partnered tarextumab in small-cell lung cancer (SCLC) after its recent failure in a prostate cancer trial, as well as anti-DLL4 antibody demcizumab which is in a Phase 2 trial in pancreatic cancer.

Like demcizumab, OMP-305B83 and OMP-131R10 are part of the stem cell-focused $3.3 billion cancer partnership with Celgene, which was signed in 2013. Phase 2 data are due next year for both tarextumab and demcizumab and will be critical for OncoMed as they will trigger opt-in decisions for both GSK and Celgene.

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