Positron emission tomography (PET) can indicate how well a thyroid tumor is responding to treatment with vandetanib. This agent, which is currently being tested in clinical trials, inhibits the function of the rearranged-during-transfection protein (RET) protooncogene and other protein kinases involved in the development and progression of cancer.

The effectiveness of vandetanib is usually measured by changes in tumor size.  Based on the agent’s effect on many intracellular metabolic pathways, however, a team of nuclear medicine experts hypothesized that metabolic imaging could be a useful—and noninvasive—method for detecting early response to vandetanib.

The researchers first achieved metabolic imaging of the agent in vitro, through transcriptional profiling and radiotracer uptake studies of medullary thyroid cancer cells. Mice were then injected with the cancerous cells for in vivo testing. Small-animal PET and computed tomography (CT) imaging reproduced the in vitro findings of metabolic activity after 3 days.

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Eventually, PET scans were used to detect a human patient’s metabolic response to vandetanib at 12 and 24 weeks after treatment.

“Our results suggest that PET may be useful for identifying patients who respond to vandetanib early in the course of treatment,” wrote the investigators in The Journal of Nuclear Medicine (2011;52[2];231-240).