Current statistics show there are 3.5 million women in the United States living with breast cancer today, and approximately 330,000 new cases are diagnosed each year. Of these new cases, 81% are identified as invasive cancers (1). About 41,000 women die from breast cancer each year (1). Thankfully survival rates have increased over the years (2); however, an accurate diagnosis and treatment plan remain essential factors for patient survival and longevity. Sometimes breast cancer patients present to their Medical Oncologist with a clinical dilemma on how they should treat their particular breast cancer, especially when standard treatment options fail. Some breast cancer tumors respond to treatment, while others do not. Knowing the type of breast tumor a patient has, its estrogen receptor site status, and how it might respond to therapy is vital information a Medical Oncologist needs to effectively and successfully treat their patients, ultimately improving patient outcomes and overall survival rates for their patients. A potential new Position Emission Tomography (PET) tracer 18 F -FES (Fluoroestradiol) (Currently under Federal Drug Administration (FDA) review for approval) (3) may be a valuable tool for MedicalOncologists to use to evaluate the estrogen receptor site status of their patients' primary tumor and secondary metastatic lesions in a non-invasive manner. Estrogen receptor site imaging is like getting a whole-body biopsy helping to localize all estrogen positive lesions in the body, so an effective treatment plan can be established for each patient. Estrogen receptor site imaging may be beneficial when tumor location is inaccessible or difficult to biopsy. Over the years, Nuclear Medicine has played a crucial role in providing useful information to Medical

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CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org. Complete the test online no later than September 2026. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 80% of the questions correctly to receive 1.0 CEH (Continuing Education Hour) credit. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.In September 2020, the Journal of Nuclear Medicine and Technology published a continuing education article, "Breast Cancer: Evaluating Tumor Estrogen Receptor Status with Molecular Imaging to Increase Response to Therapy and Improve Patient Outcomes," that reviewed a promising new PET tracer, 16a-18 Ffluoro-17b-fluoroestradiol ( 18 F-FES). This tracer had the potential to be a valuable tool for medical oncologists and breast surgeons in noninvasively evaluating the estrogen receptor site status of their patients' recurrent tumor and secondary metastatic lesions. In May 2020, 18 F-FES received Food and Drug Administration approval and began being marketed by Zionexa using the trade name Cerianna and manufactured by PETNET. In May 2021, GE Healthcare acquired Zionexa, and Cerianna and is now being marketed by GE Healthcare and is still being manufactured by PETNET. This article will review the 18 F-FES package insert information and imaging protocol, as well as important guidelines for imaging with 18 F-FES.