Researchers from the University of Wisconsin School of Medicine and Public Health have discovered a new way to measure the efficacy or failure of hormone therapy for breast cancer patients. A study detailing the findings was published in the February issue of The Journal of Nuclear Medicine.

The findings showed that positron emission tomography (PET) imaging with 18F-fluorofuranylnorprogesterone (18F-FFNP) has been found to successfully measure changes in progesterone receptor (PR) levels resulting from a short-course estrogen treatment, also known as an estradiol challenge.

Estrogen-receptor (ER)-positive breast cancer is the most common class of breast cancer, affecting nearly 70% of patients. By participating in an estradiol challenge, physicians can determine the likelihood of potential benefit of hormonal therapies targeting ER for individual patients.

As such, several PET tracers have been developed to monitor and analyze changes in the PR level during therapy.

"Typically, anatomic size and proliferation biomarkers are analyzed to determine endocrine sensitivity," Amy Fowler, MD, PhD, assistant professor, Section of Breast Imaging, Department of Radiology, University of Wisconsin-Madison, said in a release. "However, non-invasive detection of changes in PR expression with 18F-FFNP during an estradiol challenge may be an earlier indicator of the effectiveness of a specific hormone therapy."

Findings from the study show that T47D human breast cancer cells (cells with estrogen and progesterone receptors, but without human epidermal growth factor receptor-2) and mice bearing T47D tumor xenografts were treated with estrogen to increase PR expression. The cells and mice were imaged with 18F-FFNP, and assays were conducted for cell uptake and tissue biodistribution.

To investigate the separate role of PR-A and PR-B isoforms on overall 18F-FFNP binding, triple-negative MDA-MB-231 breast cancer cells were engineered to express either PR-A or PR-B. In vitro 18F-FFNP binding was measured by saturation and competitive binding assays, while in vivo uptake was measured with PET imaging.