It’s disappointing to learn from the ASCO 2013 GU symposium abstracts published today that Bristol Myers Squibb’s tyrosine kinase inhibitor, dasatinib (Sprycel), has failed in prostate cancer.
Dasatinib now joins a large graveyard of cancer drugs that showed promise in early clinical development in solid tumors, yet the data was not confirmed in a large scale randomized phase 3 trial.
The phase 1 / 2 trial results for dasatinib in advanced prostate cancer were published by John Araujo, MD and colleagues last year in the journal “Cancer” (Jan 1, 2012).
The paper concluded on the basis of two trials with 46 men that “the high objective response rate and favorable toxicity profile are promising and justify randomized studies of docetaxel and dasatinib in castration-resistant PC.”
Fast forward to the dasatinib phase 3 trial results published at ASCO GU 2013, where the data from a large scale randomized trial involving 1,522 men with advanced prostate cancer showed no significant difference in survival between men receiving dasatinib plus docetaxel (chemotherapy) versus men receiving docetaxel alone. The median survival between the two treatment arms was 21.5 vs 21.2 months (HR 0.99 P=0.90).
As the FDA comes under pressure to grant approval to promising cancer drugs based on early clinical trial data, the failure of dasatinib reminds us why large randomized trials are needed to show that a drug truly works, and the potential nemesis that may occur if phase 2 hubris alone is relied upon.
The news of dasatinib’s failure in prostate cancer is a disappointing result, but does not affect it’s role in CML where it is already approved.
Update Feb 13 – dasatinib may be effective in a subset of patients
I corresponded by email today with Evan Yu, MD, Associate Professor of Medicine & Oncology at the University of Washington School of Medicine and one of the co-authors on the dasatinib abstract presented at ASCO GU 2013.
BSB: Do you have any thoughts on why the phase 1/2 trial was promising yet the phase 3 trial ends up a failure?
Dr Yu: The challenge comes from identifying patients who have tumors that are being strongly driven by SRC. The phase 2 monotherapy data was promising, but the greatest effect was on bone turnover. And we know that SRC is expressed on
osteoclasts. The phase 1/2 combination docetaxel with dasatinib trial also showed promising results. However, it was a single arm trial without randomization. The phase 3 trial was definitely solid, well-run, and BMS should be congratulated for running such an impressive trial.
BSB: Given there was a good scientific rational for targeting Src, any thoughts on what happened from a scientific perspective that might explain the lack of any survival benefit?
Dr Yu: One must ask whether overall survival was the right endpoint for this trial? My suspicion is that the drug has potent effects in the bone for most patients, but significant direct antitumor effect for a small subset that is yet undefined. Hopefully, smaller translational studies down the road performing tumor biopsy analysis and quantitative fluoride PET imaging will help identify those populations.
Dr Yu’s perspective highlights the challenge of oncology drug development, where increasingly companies need biomarkers to identify those patients who are likely to respond and to monitor the response to treatment. His comments add weight to the notion that companies need to spend more time in phase 2 development before rushing to costly, large-scale phase 3 trials. If you don’t know who is likely to respond to your drug, then you run the risk that those who don’t respond will turn your trial into a negative result.
Update Feb 15, 2013 – dasatinib fails to show a survival benefit in any subgroup
There is additional commentary from the presentation of the dasatinib READY phase 3 trial results in my piece on Xconomy about the prostate cancer drug winners and losers at ASCO GU.