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Quest Conversion of my PCR

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#1 Johnc


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Posted 23 September 2012 - 08:00 AM

I received my PCR results under the new Quest IS. It read 27.432%. It did not reference the log reduction relative to my previous PCR. I want to walk through some deductive reasoning here to determine if this rational makes sense where I am at relative to my diagnosis and first PCR at 3 months.

My last PCR(at 3 month dx) had a small log reduction of -0.026

It states on the new Quest lab report that at 10% reading  is equal("although not precisely equivalent") to 1 log reduction, 1% is equal to a 2 log reduction and 0.1% is equivalent to a 3 log reduction. If i compute the delta(log) between 27.432% and 10% then a 1 log reduction is equivalent to needing to reduce my readings by 0.438 log reduction.

Therefore can I conclude that to date from Diagnosis that I have achieved 1 - .0438 = -0.56 reduction? My Oncs goal at 3 months was a 1 log reduction which from my calculations should they make sense was -0.56 in a 5 month period.

I asked the Onc what the new reduction was and he only said it was not a 1 log reduction but did not have paperwork in front of him as we agreed that if I did not make the reduction he would change medicine. At 3 months he wanted to change the medicine and I said lets give it another month. He was not real happy with me on this but agreed to do it

He wants to change me from Gleevec to Sprycel because of this slow response. I have absolutely no side effects from Gleevecs and hope I do as well on Sprycel. I asked if it was because of mutation or I was starting from such a High WBC of 258k. He indicated he was not sure.

Your opinions on the calculations/deductive reasoning  above would be appreciated.


#2 Trey


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Posted 23 September 2012 - 08:37 PM

Your 3 month PCR log reduction of -.02log is so tiny as to be statistically insignificant, so any extrapolation from insignificance yields no useful data.  Plus you did not say if the first was a personal log reduction calculated from your diagnostic PCR, or from some lab average.  If it was a personal log reduction, then comparing personal log reductions with IS lab average reductions (as all IS log reductions are) is also not very useful. 

#3 PhilB


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Posted 24 September 2012 - 05:14 AM

Your calculations are fine - Log10 of 27.4% is -0.56 ie a 0.56 log reduction.

The more fundamental question is, is this relevant?  This early in your treatment the important numbers to be looking at are from cytology or FISH tests.  Given your lack of side effects I'd want to see some FISH numbers before deciding on any switch of drugs.  If your 6 month FISH is below 35% then there should be no particular urgency to move to something that may, or may not, give you worse side effects.

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