Nov 08, 2011 - 1:25 am
"Who Should Be Tested
"...31-35% of patients treated with 5FU develop severe toxicity reactions. The enzyme largely responsible for metabolism of 5FU is the DPD enzyme. A deficiency of this enzyme causes the 5FU to linger in the system rather than passing through; the build-up of 5FU can be toxic. Complete DPD toxicity is rare, occurring in only 1% of the population, but for that 1%, 5FU can be fatal in just one dose. However, 3%- 5% of all cancer patients are partially deficient in DPD– and of those who experience severe toxicity, 43-59% are DPD deficient.
A National Institutes of Health paper from 2007 went so far as to recommend that any patient suspected of DPD deficiency NOT receive 5FU chemo due to life-threatening toxicity: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2563423/. Warnings have been added to labeling of both 5FU and oral Xeloda which state that these drugs are contraindicated for patients with known DPD deficiency."
A random reply to the blog above lists inexpensive testing available (from 2010) at this lab: http://www.ittlabs.com/professionals.html ...
Another lab link: https://www.myriadpro.com/test-offerings/chemotherapy-management/theraguide
1% equates to around 10,000 patients per year being completely deficient in the enzyme, with 1% of anal cancer patients being around 6-7 patients per year given the current yearly Dx numbers. 10,000 or 7 is far too many deaths from chemo toxicity when it is totally predictable, and preventable.
I think the DPD test should be standard for everybody prior to 5FU Tx, and also during Tx. As mentioned in one of the above sites, even for those many patients (31-35%) that will be discovered to be somewhat deficient in the enzyme via DPD testing and who can be predicted in advance to have a more severe reaction to it, the 5FU dosage can be adjusted accordingly as needed at the start and throughout Tx. For the other 1% that can easily be identified prior to Tx, a different chemo can be used.
I hope we all continue to speak up and keep one another informed. We are the front line.
Best wishes for us all...