The use of a positron emission tomography (PET)-based estradiol challenge test was found to be highly predictive of response to endocrine therapy in women with estrogen-receptor (ER)-positive breast cancer.

In the phase 2 study (NCT02455453), data from which were published in Nature Communications, the investigators measured the responses to endocrine therapy by monitoring the change in tumor uptake of the progestin analog 21-[18F] fluorofuranylnorprogesterone (FFNP) before and after a 1-day estradiol challenge.

The researchers hypothesized that this brief estradiol challenge would increase tumor progesterone receptor levels only in tumors with functional estrogen receptors, thereby allowing the team to identify which tumors would respond to endocrine therapy.

Continue Reading

The study included 43 postmenopausal women with advanced ER-positive breast cancer. The median patient age was 60 years. An increase in tumor FFNP uptake was seen in 28 patients with clinical benefit from endocrine therapy, defined as no disease progression within 6 months. These patients were considered to be responders.

Fifteen women were considered nonresponders. Each of the women were found to experience disease progression within 6 months of initiating endocrine therapy. 

The median percentage change in tumor FFNP uptake among responders was 25.4%; in nonresponders, it was –0.7%. These results indicate a 100% sensitivity and specificity, according to the researchers.

No adverse or clinically detectable pharmacological effects were associated with FFNP administration and there were no significant changes in vital signs.

“While the results of this study are extremely promising, our findings need to be confirmed in a multicenter trial before this method can be used to guide ET in clinical practice,” Dehdashti et al concluded.

Disclosures: Some of the study authors disclosed financial relationships with the pharmaceutical industry and/or the medical device industry. For a full list of disclosures, please refer to the original study.


Dehdashti F, Wu N, Ma CX, Naughton MJ, Katzenellenbogen JA, Siegel BA. Association of PET-based estradiol-challenge test for breast cancer progesterone receptors with response to endocrine therapy. Nat Commun. 2021;12(1):733. doi:10.1038/s41467-020-20814-9