Dr Mouabbi on the Role of FES-PET/CT in the Diagnosis of Lobular Breast Cancer

“It’s important to understand that FES-PET/CT is not meant to monitor treatment response. FES-PET/CT is meant to be done at [a certain] point in time to give us an answer to something.”

Jason A. Mouabbi, MD, an assistant professor in the Department of Breast Medical Oncology, Division of Cancer Medicine, as well as an assistant professor in the Department of General Oncology, Division of Cancer Medicine, at The University of Texas MD Anderson Cancer Center, discussed the role of 18F-fluoroestradiol (FES)–PET/CT imaging in the diagnosis of lobular breast cancer.

FES-PET/CT is not intended to be used to monitor a patient’s response to treatment, Mouabbi began. Instead, the imaging modality should be used to answer clinical questions at specific time points, he explained. For example, in patients with early-stage disease, FES-PET/CT can be used to see is the cancer has metastasized to distant location, he noted.

FES-PET/CT is not an appropriate approach for diagnosing primary breast cancer or for staging disease in the breast or lymph node, Mouabbi said. However, it can be used for distant imaging outside of the breast and the regional nodes, he noted. The technology can be used in place of a biopsy or in conjunction with a biopsy to determine if a bone lesion is hormonal or nonhormonal, he added. It can also be used in the presence of brain lesions when avoiding a brain biopsy is preferable, he said.

One of the most useful roles of FES-PET/CT is that it is the only tool that is currently available that can predict a patient’s response to endocrine therapy with or without targeted therapy, Mouabbi explained. Moreover, if a patient experiences disease progression on a frontline hormonal agent, FES-PET/CT can be used to inform the selection of treatment with either another line of hormonal therapy or moving to a cytotoxic agent such as chemotherapy or an antibody-drug conjugate, he added.

Mouabbi noted that in Version 5.2025 of the National Comprehensive Cancer Network Clinical Practice Guidelines in Oncology for breast cancer, FES-PET/CT was added as “useful in certain circumstances” as an imaging approach for systematic staging for patients with estrogen receptor–positive disease and lobular histology.