College of American Pathologists
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  Why monitor oncology drugs?


CAP Today




October 2009
Feature Story

At the AACC session, Dr. Clarke explained why it’s worth considering monitoring blood levels of oncology drugs.

The basic approach for dosing any drugs is based on mg/kg—heavier patients need heavier doses, to put it crudely. But while crude may work on “Family Guy,” drugs are another matter. That appears to be the case for oncology drugs especially, Dr. Clarke says, pointing to a 2001 study that showed the efficacy rate for a number of classes of drugs from analgesics to SSRIs to oncology drugs (Spear BB, et al. Trends Mol Medicine. 2001;7:201– 204). Response rates for the latter category were reported to be about 25 percent.

Why the poor response?

Choose a reason, Dr. Clarke suggests:

  • Cancer is a heterogeneous disease.
  • Because of evolving mutations, rapidly growing cancer cells quickly become dedifferentiated.
  • People are heterogeneous, with genetic variability in their metabolisms and in other pharmacokinetic parameters.
  • Oral chemotherapy agents can “self-affect” PK—inflammation in the GI tract, for example, can alter absorption of the drug.
  • Some patients are noncompliant with oral chemotherapy.
  • Many patients are on multiple drugs, with the possibility of drug-drug interactions.
All those factors may throw target or reference intervals out of whack. Such levels are established through clinical studies. But while reference levels are population-based, patients are not. “When we talk about personalized medicine, we’re taking a population-based therapeutic target as our starting point,” says Dr. Clarke.

—Karen Titus


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