UPDATED: Celldex's cancer vaccine Rintega implodes in glioblastoma PhIII

Celldex CEO Anthony Marucci

Celldex's Rintega (rindopepimut) has proved to be a bust in glioblastoma. The biotech reported this morning that it is cutting a Phase III study short after independent monitors concluded that the drug failed the endpoint for improving overall survival.

The biotech's shares ($CLDX) immediately plunged 66% as investors reacted to the disaster, which surprised some analysts. Last summer, for example, Roth Capital analysts predicted that Rintega was on a path to becoming the second cancer vaccine approved in the U.S., following Provenge, which proved to be a colossal commercial disappointment. And those who had been disappointed when Celldex failed to seek an accelerated approval based on Phase II data were particularly disappointed this morning.

"This result was a surprise negative disappointment on the primary driver of value in our model," noted Seamus Fernandez at Leerink. "While we recognize that Rintega's market opportunity was relatively narrowly defined (~30% of glioblastoma), removal of the projected revenues has a large impact on our earnings projections, as CLDX's R&D spend & headcount suggest significant risk of future dilution." 

Celldex had built hopes for the drug around a Phase II study that looked promising for patients with EGFRvIII-positive glioblastoma. Looking at progression-free survival, the drug scored a higher PFS rate than the control arm. But investigators concluded at an interim analysis in the Phase III that the control arm was doing slightly better than the drug arm.

The Hampton, NJ-based biotech reported that patients in the drug arm achieved a median OS of 20.4 months while the control arm survived 21.1 months.

Brain cancer has long proven to be a thorny problem for drug developers and is typically a death sentence for patients. Celldex had hoped that it could also overcome a poor record for cancer vaccines by revving up an immune system assault on the EGFRvIII protein found on the surface of glioblastoma cells. 

The target is found in about 30% of all glioblastoma tumors. And the latest setback in the field is likely to raise fresh questions for Northwest Biotherapeutics, which has its own cancer vaccine--DCVax--in development for glioblastoma.

"While this is certainly not the desired outcome, we remain steadfast believers in the power of immunotherapy to transform the future of cancer treatment," says CEO Anthony Marucci in a statement.

- here's the release