With the exception of liver metastases, whole-body imaging of estrogen receptor (ER) expression with 18F-FES, an ER-specific PET tracer, can be a valuable additional diagnostic tool when standard work-up is inconclusive, particularly in breast cancer patients, according to a study published in the February issue of the Journal of Nuclear Medicine.
Breast cancer is the most common cancer in women in the Western world. Approximately 75 percent of the tumors express the ER at diagnosis. Knowledge of a patient’s ER status, according to the study authors, has important consequences for treatment decision making, because patients with ER-positive tumors are likely to respond to anti-hormonal therapy.
“The precise contribution of this technique in current clinical practice, however, has yet to be determined,” they wrote. Therefore, Michel van Kruchten, MD, MSc, from the department of medical oncology at the University Medical Center Groningen in Groningen, The Netherlands, and colleagues conducted this study to evaluate the value of 18F-FES PET in breast cancer patients presenting with a clinical dilemma.
In the study, an 18F-FES PET exam could be requested by referring physicians for patients with a history of ER-positive breast cancer and the presence of a clinical dilemma despite complete standard work-up. All requests for 18F-FES PET required a positive arbitration by a dedicated medical oncologist and nuclear medicine physician. The referring physician was asked to fill in validated questionnaires before, shortly after and at more than three months after 18F-FES PET to determine indication, diagnostic value and therapeutic consequences of 18F-FES PET. To further validate the 18F-FES PET findings, the researchers quantified and compared 18F-FES PET lesions with centrally reviewed conventional imaging.
Kruchten et al reported that 33 patients underwent 18F-FES PET between December 2008 and October 2010. 18F-FES PET was requested to evaluate equivocal lesions on conventional work-up (21 patients), ER status in metastatic patients (10 patients) and the origin of metastases (two patients).
The researchers observed that 18F-FES-positive lesions were observed in 22 patients. 18F-FES PET was especially sensitive for bone metastases, detecting 341 bone lesions, compared with 246 by conventional imaging. The sensitivity for liver metastases was poor, and quantification of 18F-FES uptake in liver lesions was hampered by high physiologic background.
According to the study authors, 18F-FES uptake was highly variable between all metastases, and 45 percent of the patients with a positive 18F-FES PET finding had both 18F-FES-positive and 18F-FES-negative metastases.
Also, 18F-FES PET improved diagnostic understanding in 88 percent of the patients and led to therapy change in 48 percent of the patients.
Based on their findings, Kruchten et al concluded that 18F-FES PET supported therapy decisions by improving diagnostic understanding and providing information on ER status of tumor lesions, except for liver metastases. Thus, they recommended that the “therapeutic consequences of having heterogeneous 18F-FES uptake and the influence of background estrogen levels should further be explored.”