Bob, safety and efficacy both I think, but with emphasis on safety on the basis that good clinical practise seems to be to err on the side of not making things worse and injuring the person more than the disease is harming them. That is a reasonable approach, especially given the litigious nature of the USA.
Radiation treatment by either external beam or injecting radionucleides is limited by marrow damage, leukeamia, thyroid cancer etc. Bone absorption is a characteristic of Yttrium which I131 doesn't have. This favours Coulter's Bexxar - though each says their approach is safer.
Heck, I wouldn't say they botched the Phase I trial. It just seems to me that the end result might be more Yttrium and no cold Rituxan. Though as Webhead says [with lots of credentials to back it up] these CD20 antigens have some sort of half life, so the 'protective coating' is maybe relatively short and inconsequential.
The problem I have with that is that half lives work by half the substance changing after a certain stable time. I131 half life is 8 days, so if you start with a million atoms of it, after 8 days you have 500,000, after 16 days 250,000, after 24 days 125,000, 32 days 62,000, 40 days, 31,000, 48 days = 15,500, 56 = 7,700, 64 = 3,300, 72 = 1,600, 80 = 800, 88 = 400, 96 = 200, 104 = 100, 112 = 50, 120 = 25, 128 = 12, 136 = 6, 144 = 3, but things go wrong here because it is a statistical game and a single radionucleide might not degrade for years! So it isn't necessarily all gone by going out to 200 days.
In the body, excretion is a rapid remover of I131, so it is all gone before it all gets a chance to degrade, but my point is the half-life concept.
If the same 'half-life' process applies to CD20 antigens on cancer cells, then after maybe 10 days maybe 80% have re-expressed CD20 - or whatever the 'half-life' is. So maybe after 3 months, there is still an unreproduced cancer cell with Rituxan protection of CD20 antigen sites, which might have escaped treatment and goes on to kill.
This all being total conjecture in the absence of facts, I emphasize, lest anyone with less understanding than I have think that I know what's going on. Anyone who knows what's going on, please feel free to set me straight.
My point is, do intermediate grade CD20 B-cell NHLs get 'hardened' against Y2B8 attack by a coating of cold Rituxan? If there is a half-life for this protection, how long is the half-life?
Webhead or anyone, any information appreciated.
Maurice
PS: Yes, they take marrow samples, one from each side of the pelvis and these are not definitive, there being a lot of places where marrow might exhibit cancer.
Bob, please bear in mind with my posts, that I'm not telling you what half-lives are etc, just thinking out loud and trying to make the posts self-explanatory for others who might not know what a half-life is. Nobody I know wants a half-life! |
