On the surface the maths you've done makes sense. However I think there is a little more to it which means that actually you can't do exactly what you've done to estimate the effect of the treatment.
Patients get classified by a doctor at day 28 of the trial as either responder or non responder. Those classified as responders get an additional 4 weeks of treatment compared to non responders. So the comparison of 81% vs 39% is comparing two sets of patients who both received the same treatment type, but with one group of patients receiving an additional 4 doses. So in this trial there is no comparison of treatment vs control, there is only a comparison of two sets of patients with one set getting double the dose of the other, and whether this happens or not is decided by the doctor at day 28. I'd say this trial design is deliberate because of the patient population being considered here (extremely ill young children). The classification of "non responder" doesn't actually mean it is not working at all, but rather the doctor has decided there is little point giving an additional set of doses, at least in this trial.
So in a sense it is difficult to determine the true efficacy of the drug from the trial. The only real recourse that I can see is that we have is to go to the literature to find baseline survival rates by GVHD grade and compare to the final outcome.
In this case grade D GVHD have survival rates of around 5-10%, and grade C of around 20-30%. In this trial day 100 survival for Grade D GVHD was 50%, and for grade B/C was 80%.
It is important to note that day 100 survival is thought to be a good predictor of long term survival (which is why this assessment period was used). I have to say it is a little interesting that the non responders actually survived so well. Perhaps the classification of what makes a responder was not so good, perhaps just getting more doses really made the big difference. I can't see how it is possible to tell these things from trial alone.
I think the main point of the trial is that it works. The lack of a control group is noted in the published announcements and literature. Better figures will come out once it is being used in clinical practice.
BTW I liked your post, it makes logical sense from some of the limited information available. I wouldn't want anyone to get carried away either. I've posted before this comment - for me it isn't the revenues so much that matter to me, it's more getting the first product to market. In the long run revenues from GVHD will be small compared to the other products.
MSB Price at posting:
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