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Biotech / Medical : Biotech Valuation
CRSP 56.68-2.4%Dec 12 9:30 AM EST
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To: Icebrg who wrote (9245)10/1/2003 12:39:29 PM
From: Biomaven  Read Replies (1) of 52153
 
Erik,

Neither drug is going to work on all tumor cells in all patients. If you assume Tarceva/Iressa have some efficacy as monotherapy then you have to come up with some explanation of why they don't help when added to chemo. There are a number of possible explanations (but I'm talking here without much in the way of specific knowledge):

1. One unlikely explanation is that they are "dominated" by the chemo drugs - in other words they only help patients who would have been helped by the chemo anyhow. This seems unlikely because of the different modes of action and because of the fact that some patients who didn't respond to chemo still respond to Iressa.

2. A second explanation is that the drugs interfere with each other in some way. It's plausible that the EGFR drugs interfere with the efficacy of chemo, and there might be a subtle timing interaction - the combo might work much better if you alternate the drugs rather than give them at the same time. (Thus if a tumor cell escapes from the G1 phase block after a few days it would run into the chemo - as it is, by the time it escapes, the chemo might no longer be on board). It's also possible that the chemo hurts the efficacy of the EGFR drugs by breaking some existing checkpoint mechanism.

Peter

P.S. A nice animated diagram of the cell cycle can be found at:

cellsalive.com
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