"Do or do not. There is no try."
2010 looks to be a good year for prostate cancer after a six year wait since the last therapy (docetaxel) was approved for what was then known as hormone refractory (now called castrate resistant) prostate cancer, or CRPC, for short.
This year has already seen two new approvals for the disease, namely:
- Sipuleucel-T (Provenge) from Dendreon in asymptomatic or mildly symptomatic CRPC prior to chemotherapy.
- Cabazitaxel (Jevtana) from sanofi-aventis in docetaxel failure CRPC.
In addition to these, we have also seen new data for two other novel hormonal therapies, namely abiraterone (Cougar/J&J) and MDV3100 (Medivation/Astellas) in the CRPC setting.
MDV3100 is now entering phase III trials in the 2nd line and asymptomatic setting, while the phase III data was presented on abiraterone here at ESMO yesterday in the Presidential Symposium.
Abiraterone was originally developed by the Institute of Cancer Research (ICR) in the UK and is a CYP17 steroid inhibitor that prevents the biochemical conversion of cholesterol to testosterone. Testosterone is secreted by the testes, adrenal gland and prostate tumour to ensure it's growth and survival via androgen receptor (AR) signalling. The simple idea here is that biochemically inhibiting the key pathways with both abiraterone and a steroid such as prednisone or dexamethasone, will lead to improve outcomes for men with prostate cancer.
The proof of the pudding lies in a randomised phase III trial to determine whether the combination is both safe and effective.
The results were interesting, to say the least.
The overall survival (OS) was as follows:
- Abiraterone + prednisone: 14.8 months
- Placebo + prednisone: 10.8 months
The PSA response also favoured the treatment arm:
- Abiraterone + prednisone: 38.0%
- Placebo + prednisone: 10.1%
Adverse events with abiraterone treatment were obviously higher than for placebo, but in general it appeared well tolerated and an important common side effect was fluid retention (30.5% of patients, with 2.4% of them being severe ie grade 3/4 in severity).
No data on the circulating tumour cells was given at this meeting, but the analysis is underway and will be published in 2011.
The big questions that spring to my mind are how do these results stack up against what we have and is the control arm ideal?
Cabazitaxel was approved earlier this year in combination with prednisone versus mitoxantrone plus prednisone, with an OS benefit of 2.8 months. Previously, mitoxantrone was approved in 1996 with a survival benefit over prednisone. Other therapies were not so lucky – GPC's satraplatin showed no benefit at all over prednisone.
If we look in the absolutes, the 3.9 month benefit for abiraterone sounds great until we look at the relative vales and comparators in more detail:
2nd line metastatic setting:
- Satraplatin vs prednisone: 14.3 vs 14.3 months
- Cabazitaxel + pred vs mitox + pred: 15.1 vs 12.3
- Abiraterone + pred vs prednisone: 14.8 vs 10.9
Mitoxantrone generally offers some benefit over prednisone, based on the original head to head trial, leading it to become the first chemotherapy to be approved for advanced prostate cancer by the FDA. I've no idea why mitoxantrone plus prednisone was not used as the control group instead of prednisone alone, but we can only evaluate what we have.
You have to say, based on this top line overview, GPC were really unlucky to have a placebo group do uncommonly well! An OS of 10-12 months for prednisone might well be a most logical expectation, but that's how clinical research goes sometimes.
It's odd, but had the abiraterone control group done as well as satraplatin's control, the outcome difference would likely be minimal and not significant. Such is the crapshoot we call R&D! Overall, my sense is that mitoxantrone plus prednisone does better in terms of OS than prednisone alone, so we would expect abiraterone's control group to be lower than cabazitaxel's, making the relative difference higher, and that is indeed the case based on the data so far.
Still, we also have to think about this from the patient perspective. Many men are like my own Father was – they would much rather pop a pill or have an injection than go through chemotherapy and risk feeling sick and have their hair fall out. Indeed, I suspect he was typically of many 70 year olds who declined chemotherapy, but might have considered abiraterone or sipuleucel had they had been available ten years ago.
If you're wondering what will happen next, well according to the press releases, J&J will be submitting the filing to the regulatory authorities by the end of the year, which means we should know some time in 2011 whether we will have a 3rd active drug approved for this cancer.