Overview of Estrogen Receptor-Targeted Imaging

Gary Ulaner, MD, PhD: Thanks for that excellent introduction to estrogen receptor–positive breast cancer and the ways that we would typically evaluate the estrogen receptor status, such as through biopsy. As you said, biopsy is not always attainable or desired, so it would be great if we had a noninvasive way to assess estrogen receptor status. What we have is called molecular imaging and therapy, and it’s developing into a tremendous field for medicine. Imagine, on the right, we see a cancer cell such as the breast cancer cell, and each cancer cell expresses unique targets, either on the surface or within the cell. We’re able to design binding agents that bind to that target much like a key fitting into a lock. And if we linked to that binding agent a radioisotope, something that emits a small amount of radiation, we’re able to build the keys that act as imaging agents for us to identify and localize where specific targets are on a cancer cell.

We’re going to be talking about estrogen receptor–positive breast cancer imaging, where the cancer cell is the breast cancer cell, the target is the estrogen receptor, which is found within about 75% to 80% of breast cancer cells. The binding agent is estradiol, in the upper left. Estradiol is estrogen, which is already found physiologically in our bodies. A radioisotope has been linked to estrogen, the radioisotope called fluorine-18, which emits a positron, which we’re able to visualize and localize in a PET [positron emission tomography] scanner.

Thus, we’re able to develop this key, which consists of estrogen as its binding agent, and fluoroestradiol as the radioisotope that allows us to image the estrogen and produce exquisite images of where estrogen receptor is within the body, such as the example on the lower right of the screen, demonstrating the sites of estrogen receptor–positive breast cancer in a way that is first a whole body. You can image from head to toe if you want to.

Second, it’s noninvasive—no biopsy, no needle required. This FES key we’re using for molecular imaging has been studied for quite some time, and data have been able to demonstrate that this allows us the noninvasive, whole-body assessment of estrogen receptor expression that we can use in lieu of biopsy to evaluate estrogen receptor. This compilation of work has led to FDA [Food and Drug Administration] approval of FES as an agent known as Cerianna for the whole body, noninvasive evaluation of estrogen receptor.

Transcript Edited for Clarity