Abstract
357
Introduction: Endometrial cancer is the most common gynecological malignancy. Molecular imaging with 18F-fluorodeoxyglucose (FDG) PET/CT has been used for the evaluation of patients with suspected metastatic disease via the visualization of lesions with increased glucose demand. The main known limitation of FDG stems from its fast urinary excretion. Intense tracer washout through the urinary tracts, and especially the bladder, may hamper the evaluation of malignant pelvic structures. 18F-Fluciclovine is a novel synthetic amino acid PET radiotracer that has been approved for the evaluation of suspected prostate cancer recurrence. 18F-fluciclovine is a known substrate of amino acid transporters such as LAT, which is upregulated in endometrial cancer cells. Bladder excretion of 18F-fluciclovine is minimal, which potentially allows a higher tumor-to-background ratio in patients with endometrial cancer. Our goal was to characterize 18F-fluciclovine uptake in patients with known endometrial cancer.
Methods: Patients with biopsy-confirmed primary or recurrent endometrial cancer underwent a dual time-point 18F-fluciclovine PET/CT scan using two minutes per bed position. Early images were obtained at 4-22, and delayed images were obtained at 24-42 minutes. Standardized uptake values (SUV) of suspicious lesions and background structures such as the lower abdominal aorta, bone marrow (L3 vertebrae), liver, and bladder were recorded. The reading criteria for suspicious uptake was adopted from the Axumin prostate cancer interpretation guidelines. Lesions were specified as suspicious when SUVmax was above the SUVmean of L3 marrow on early and delayed images. Histology was used as a verification method. Time-activity curves plotted the averages of tumor SUVmax and background structures SUVmean. The PET/CT scan sensitivity was calculated.
Results: Seven subjects prospectively underwent an 18F-fluciclovine PET/CT scan. Primary endometrial cancer was present in 3/7 subjects, while 4/7 had a recurrence. 18F-fluciclovine PET/CT yielded 100% sensitivity with 18 indexed true positive lesions. 6 lesions were local (uterus/uterine bed), and 12 lesions were extra-uterine. The average SUVmax (± SD) uptake in the malignant lesions was 5.65 ± 1.31 and 4.79 ± 1.40 on early and delayed images, respectively. The average SUVmean (± SD) of background structures on early and delayed images was 3.94 ± 0.84 and 3.04 ± 0.57 respectively for marrow and 1.84 ± 0.27 and 1.56 ± 0.24 respectively for the aorta. No bladder tracer washout was noted on the early images with SUVmean (± SD) of 0.67 ± 0.31 compared to the delayed images with SUVmean (± SD) of 1.93 ± 1.04.
Conclusions: Malignant endometrial lesions demonstrate marked 18F-fluciclovine uptake compared with background structures. Early time-point images at 4-22 minutes allow a better tumor-to-background ratio due to low tracer washout through the bladder.