topic : drugs to watch at 2013 ASCO" by Ohad Hammer
"Exelixis (EXEL) will have several clinical updates for cabozantinib (Cometriq) in different indications. Although none are expected to have a major impact on the stock, they could provide some read-across for the ongoing phase III in prostate cancer as well as insight on activity in RET-mutated tumors.
Survival data from prostate cancer phase II – Updated results from a single-arm phase II in prostate cancer will be reported. By definition, analyzing results from non-comparative trials is problematic but the trial was fairly large (144 patients). As background, this was the trial that demonstrated the drug’s controversial bone scan normalization effect (reviewed here).
The abstract reports a median survival of 10.8 months, which is encouraging given the tough patient population (73% were ≥3rd line, many were taxane resistant/refractory). The most important read across is for the ongoing phase III trial, as investors will try to put cabozantinib’s survival in context with Zytiga’s and Xtandi’s post-chemo survival (with the caveats of cross trial comparisons).
Since patients in cabozantinib’s phase III are Zytiga and/or Xtandi failures, cabozantinib’s phase II data can be compared to the post-treatment survival in the phase III studies for both agents (8.5-10 months). At ASCO, survival for the Zytiga pre-treated subgroup will be particularly relevant as this subgroup more closely resembles the population being enrolled in the Phase 3 trial.
At first glance, cabo’s 10.8 months does not look impressive but it appears cabozantinib phase II had a much tougher patient population based on prior therapies and resistance to taxanes (Taxotere or Jevtana). In particular, all patients had progression within 6 months of last taxane dose and more than a third of patients progressed within 1 month after last taxane dose (highly aggressive tumors)."