Exelixis has suffered a hammer blow with the news that its investigational prostate cancer drug has failed a late-stage trial, prompting the need to cut its workforce by 70%.

The Phase III trial involved men with metastatic castration-resistant prostate cancer (mCRPC) whose disease progressed after treatment with docetaxel as well as with Johnson & Johnson’s Zytiga (abiraterone) and/or Astellas' and Medivation's prostate cancer drug Xtandi (enzalutamide). The study did not meet its primary endpoint of demonstrating overall survival  for patients treated with cabozantinib as compared to prednisone.

The median OS for the cabozantinib arm of the trial was 11.0 months versus 9.8 months for prednisone arm. Median progression-free survival was 5.5 months for the Exelixis drug versus 2.8 months for prednisone and Exelixis has “deprioritised” the clinical development of cabozantinib in mCRPC; a second Phase III study evaluating pain palliation has been halted, as has a Phase II cabozantinib/abiraterone combo trial.

Exelixis will initiate “a significant workforce reduction” with 160 staff being cut, leaving 70. The company will now  focus on late-stage trials of cabozantinib for advanced kidney and liver cancers; the drug was approved in November 2012 for medullary thyroid cancer in the USA where it is sold as Cometriq.

In connection with the workforce reduction , Exelixis will take a $6-$8 million charge and expects to have enough cash to support its operations through the release of top-line results of the kidney cancer trial trial next year.