Anti-3-18F-FACBC (18F-Fluciclovine) PET/CT of Breast Cancer: An Exploratory Study

The purpose of this study was to explore the uptake of the synthetic amino acid analog PET radiotracer anti-3-(18)F-FACBC ((18)F-fluciclovine) in breast lesions with correlation to histologic and immunohistochemical characteristics.

Twelve women with breast lesions underwent 45-min dynamic PET/CT of the thorax after intravenous administration of 366.3 ± 14.8 (337.44-394.05) MBq of (18)F-fluciclovine. Uptake in the primary lesions at 4 representative time points (5, 17, 29, and 41 min) after injection were correlated with histologic, imaging, and clinical findings. The significance of differences in SUVmax and tumor-to-background ratios between malignant and benign tissue were calculated. Correlations of activity to histologic and immunohistochemical cancer subtypes were made including Ki-67 intensity and Nottingham grade (NG).

There were 17 breast lesions (4 benign, 13 malignant) including 7 of 13 invasive ductal, 5 of 13 invasive lobular, and 1 of 13 metaplastic carcinomas. There was a significant difference in mean SUVmax ± SD of malignant (6.2 ± 3.2, 6.0 ± 3.2, 5.7 ± 2.8, and 5.6 ± 3.0) versus benign (1.3 ± 0.6, 1.2 ± 0.5, 1.2 ± 0.6, and 1.1 ± 0.5) lesions at 5, 17, 29, and 41 min, respectively (all P ≤ 0.0001). Tumor-to-background (aorta, normal breast, and marrow) ratios were also significantly higher in malignant than benign breast lesions (all P ≤ 0.02). The highest (18)F-fluciclovine activity seems to be present in triple-negative and NG3 subtypes. Across time points, quantitative Ki-67 had weak positive correlation with SUVmax (R1 = 0.48 [P = 0.03], R2 = 0.44 [P = 0.03], R3 = 0.46 [P = 0.03], R4 = 0.43 [0.06]). In 7 patients, (18)F-fluciclovine PET visualized locoregional and distant spread including that of lobular cancer, though identification of hepatic metastases was limited by physiologic background activity.

The uptake characteristics of (18)F-fluciclovine are reflective of the histologic and immunohistochemical characteristics in suspected breast lesions with greater activity in malignant versus benign etiology. The data from this exploratory study may be useful to design future studies using (18)F-fluciclovine PET for breast tumor imaging as well as for detection of locoregional and distant spread.