Seattle researchers say PET scans can help gauge the relative effectiveness of different types of hormone therapy for some breast cancer patients, suggesting the technology can measure in vivo pharmacodynamics and aid in drug development.

In a small study published online last month in Clinical Cancer Research, scientists with the Seattle Cancer Care Alliance said PET scans showed drugs that block estrogen receptors trumped those that merely depleted estrogen in starving estrogen-sensitive tumors of the female hormones they use to grow.

These results were expected, the researchers said, although they hadn't been shown before with this technique.
"What we're suggesting in the paper -- that we couldn't fully test for before -- is if estrogen is incompletely blocked you're not getting a good outcome for the patient," Dr. Hannah Linden, corresponding author and a breast oncologist with the alliance, said in a statement.

The study examined 30 breast cancer patients whose cancers had metastasized, and spread to the bone.

The women in the study were given PET scans before, during and after treatment, using 18F-fluoroestradiol (FES), which attaches to estrogen receptors and fires out gamma rays picked up by the PET scanner.

The women were treated with either tamoxifen or fulvestrant, estrogen-blockers, or aromase inhibitors, estrogen-depleters.

Drugs like tamoxifen work by preventing cancer cells from using estrogen. Drugs like aromase inhibitors work by reducing the amount of estrogen produced by the body, but they can only be used in post-menopausal women as they don't block estrogen production in the ovaries.

Both drug types are effective against estrogen-sensitive breast cancers. However, although research is ongoing, many recent studies have favored aromase inhibitors for post-menopausal women.

But in the current study, tumor uptake of the radiotracer fell more with tamoxifen and fulvestrant than with the aromase inhibitors, the researchers said. On average, uptake dropped 54 percent for the blockers versus 15 percent for the depleters.

However, complete tumor blockade was greater for tamoxifen than for fulvestrant, the researchers said.

"FES PET can assess the in vivo pharmacodynamics of (estrogen receptor)-targeted agents and may give insight into the activity of established therapeutic agents," the authors wrote. "Imaging revealed significant differences between agents, including differences in the efficacy of blockade by different (estrogen receptor) antagonists in current clinical use."

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