Han Li, Ph.D., 212.319.3808
• This is what ABGX/AMGN reported yesterday:
Panitumumab met the primary endpoint of improving progression-free survival (PFS) in a Phase 3 study of 463 colorectal cancer (CRC) patients who had failed prior chemotherapy. Panitumumab “showed a 46% decrease in tumor progression rate versus those who received best supportive care alone (p <0.000000001).”
Although ABGX/AMGN did not provide median PFS data for both BSC and treatment groups, management commented that the majority of patients in the Phase 3 study (408) have progressed by week-8 and 75% of patients crossed over from BSC to Panitumumab.
• This is the Erbitux data from the Bond study:
Erbitux was approved based on results from a 329-patient study (Bond 007) in refractory CRC, which showed that Erbitux + Irinotecan have a response rate (RR) of 22.9% and time to progression (TTP) of 4.1 mo. vs. Erbitux alone with 10.8% RR and 1.5 mo TTP.
• Now, based on the above data, can you draw a conclusion that Panitumumab is a superior drug to Erbitux?
Given the limited information from study 408, we find it difficult if not impossible to conclude.
We note that the 46% improvement is in tumor progression rate, NOT PFS.
There are more questions than answers about the Panitumumab Phase 3 data:
What is tumor progression rate?
What is the tumor progression rate in Panitumumab and BSC groups?
And median PFS in each group?
• We estimate that median PFS of Panitumumab in study 408 could be around 8 wks.
If we assume that 75% of BSC crossover patients had progressed by week-8, we can deduct a progression rate of 40% for Panitumumab by applying a factor of 0.54 (1-46%).
This results in a total of 58% of total patients (“majority”) progressed by week-8.
The median PFS of Panitumumab (50% of progression) should be around 8 weeks.
This is not far from Erbitux’s six week median TTP reported from the Bond study.
The two- to three-week difference could be due to the time of first scan (six weeks versus eight weeks).
• While we await detailed data from the 408 study (possibly at ASCO 2006), we believe the market overacted on the assumption of Panitumumab is a better drug than Erbitux. R
• We recommend buying IMCL on weakness.
Source:
Nov 4
www.SunTrustRH.com
Summary of Morning Meeting Comments - November 4, 2005
For complete details of morning meeting presentations, together with histories of recommendations and important disclosures,
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