[chrisy]

I'm not a molecular biologist, don't even play one on tv. I think there are many reasons why it is "trastuzumab-DM1" instead of a myriad of combinations.

First and foremost, it took them quite some time to be able to effectively attach the DM1 to the Herceptin. Don't forget the full name of the drug is T-MCC-DM1 with the MCC being a separate piece linking the DM1 to the herceptin, then releasing it into the target cell. One of the big holdups on this drug, as I understand it, was getting the linker to work - because the DM1 is so toxic you really don't want it released into the general bloodstream. I suspect that future applications would include trying to use that MCC link to attach to more of both type of molecules (the "smart" targeting agent and the "bomb" toxin). It's probably not so simple as just hooking it onto the next targeting agent (tykerb) that comes along.

DM1 is a powerful toxin, so it would probably work well on many types of cancer, the problem is it is so toxic it needs the "smart" part or it would be too toxic to use. So you'd have to find a target, then have a drug (like herceptin) that would deliver to the target. So it's more that it can only be USED on Her2+ cancer because that's the only one that they can target in this way.

Also, they do not yet really have "proof" that it works. Only now are they beginning phase III trials where they can actually compare it to other therapies. The present focus would be on proving that the Herceptin DM1 works and getting it through the approval system.

But I'd have to agree with what I think is your underlying point: I sure wish they would hurry up!