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# Exelixis, Inc. Message Board

• metropath metropath Feb 16, 2013 8:46 PM Flag

## Cabo expectation

"IF Exelxiis 6 month survival expectation is accurate, that gives you a good indication of poor prognosis in COMET 1 population..."

MDV3100 prolonged survival by a mediun of 4.8 month in the phase 3 AFFIRM trial: MDV3100 median OS 18.4 months versus placebo median OS 13.6 months.
ALSYMPCA prolonged survival by a median of 2.8 months in the phase 3 study: Radium-223 median OS 14.0 months versus placebo median OS 11.2 months.
How many months do we expect from Cabo to get FDA approval?

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• "How many months do we expect from Cabo to get FDA approval?" Before I answer your question, let's look at what all of those OS numbers represent. They are the median survival, half of the patients survive longer and half less. A survival curve is a graph of time vs the number of patients still on trial. To graphically determine median survival you enter the chart on the Y axis at the point that represents 50% of the patient population, read across to the right until you hit the curve and then read straight down to determine the median survival. A comparative trial with two arms will have both survival curves on the same graph. A comparison of the medians is just a comparison of the two survival curves at a single point. You could have a situation where the maximum separation of the curves just happens to occur at the median. In such a scenario the comparison of the medians would overstate the advantage of one cohort over the other. Another situation would be the two curves have have a minimal separation at that line that represents half of the population, but the curves have large separations before and after that 50% comparison. In that case you could have a very effective drug with a modest OS improvement in terms of increased median survival.

What I am telling you is that a comparisons of medians is an approximation of efficacy but the true measurement on which the approval hinges is based is hazard ratio which is a measurement of the risk of death over a time period. That hazrd ratio is then used to compute a p value which is the statistic that determines if a primary endpoint is attained or not attained. So back to your question, There is no single median OS advantage that will determine if Cabo is approved or not. It depends on a mathematic comparison of all the survival data and can be thought of as the area between the survival curves. The greater the separation of the curves, the lower the HR and the smaller the p value (all good). The Comet one trial is powered to show a 25% reduction in risk of death with a power of 90%. It is common practice, but not really accurate, to apply that HR directly to the assumed median survival for the control arm and come up with a needed level of efficacy for the treatment arm. In this case, the presumed efficacy for the placebo arm is 7 months. A 25% improvement is about 1.75 months, but that is at 90% power. If you figure it for 50% power. Cabo could show as little as a 1 month improvement and still get a statsig result.

• 2 Replies to erniewerner
• thaks Ernie, i understand the mdian OS and other important parameters for a new drug approval. all i just want to say is that there is no good deal yet when dealing with mCRPC. Cabo' s noval mechanisms brings the hope for either fingting alone in bone met /bone pain, and/or prolonging OS when comined with others.

• \$\$\$\$

Speaking of expectations, I pulled the following twitter quote out of the Market Pulse side of Yahoo Finance, as posted by Biotech Stock Research"

"~40% of audience members would prescribe cabozantinib in PCa if it were reimbursed. #gu13"

Any idea what these guys are referring to...?? This format exactly matches a bunch of twitters coming out of ASCO GU on Saturday, but I can't match it up to any particular event. Might be meaningless if it were a show of hands at a stoned-out Led Zeppelin concert...but it sure makes me wonder who was in that audience, and who would conduct such a survey. Still looking...

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