The National Comprehensive Cancer Network (NCCN) Clinical Practice Guidelines® in Oncology are recognized as a standard for cancer care worldwide and are used by clinicians, payers, and other healthcare decision-makers. New in 2025, the NCCN guidelines include mention of the utility of the use of the procedure FES-PET in certain instances in treating ER-positive metastatic and/or recurrent invasive lobular carcinoma (ILC)..

FES-PET is a diagnostic procedure that entails giving a patient a radiotracer dye called 18F-Fluoroestradiol (FES) intravenously and then conducting a PET scan. The FES, which attaches to cells in the body with estrogen, appear on the PET scan image resulting in an effective mechanism for imaging estrogen receptor positive (ER+) breast cancer metastases. This is the first time the NCCN guidelines identify any procedure’s utility for  ILC-specifically. The guidelines note that FES-PET can be useful for specific scenarios including:

• Helping to select appropriate patients for endocrine therapy
• Evaluating lesions that are equivocal or suspicious on other imaging tests
• Evaluating lesions that are difficult to biopsy, or when biopsy is non-diagnostic

The revision to the NCCN guidelines suggests the possible utility of FES-PET for evaluating the extent of the spread in the body of ER-positive ILC in the case of a recurrence. For more detailed information on appropriate use of FES-PET, please see the Appropriate Use Criteria (AUC) developed by the Society of Nuclear Medicine and Molecular Imaging (SNMMI) (and with the input of SAB members Drs. Gary Ulaner and Jason Mouabbi) for this imaging modality.  Form ore information, see this video about AUCs.