¹⁸F-Fluoroestradiol (FES) and¹⁸F-Fluorodeoxyglucose (FDG) PET imaging in male breast cancer

Objectives: Breast cancer is an uncommon disease in men. Because of the rarity of the disease, PET imaging results and guidelines for optimal management of male breast cancer are limited. FES is an estrogen analogue that correlates with tumor ER expression, provides assessment of multiple tumor sites simultaneously, predicts response to endocrine therapies and measures ER blockade. This study examines FES-PET and clinical FDG-PET SUV uptake in a small cohort of male patients compared to a larger group of female patients with metastatic invasive ductal carcinoma studied at our center. Methods: We retrospectively investigated differences in FES and FDG SUV uptake between male and female patients with metastatic invasive ductal carcinoma (8 male and 148 female) enrolled in various studies at our institution. Up to nine lesions in each patient were evaluated by FES SUVmax and/or FDG SUVmax for a total of 403 lesions in FES images (n=30 in men) and 292 lesions in FDG images (n=19 in men). Using mixed-effects models to account for multiple scans from the same patient, we assessed difference between males and females in both FES SUVmax and FDG SUVmax. Overall survival (OS), measured from the time of the FES-PET scan to death, was compared between males and females using Kaplan-Meier curves and the Log-Rank test. Results: Mean SUVmax in FES and FDG respectively for men was 2.9 (1.4, 6.1) and 4.6 (1.1, 9.6) and for women was 3.4 (0.53, 20.5) and 4.9 (1.1, 26.7). Difference in FES SUVmax between sexes was marginal and non-significant. On the natural log scale, males demonstrated a higher SUVmax (Difference = 0.14, 95%CI = [-0.31,0.60], p=0.54) and a lower FDG SUVmax (Difference = -0.60, 95%CI = [-3.06, 1.86], p=0.63). Regarding OS following FES-PET imaging, men had a lower, non-significant median survival time (3.2 vs 4.5 years, p = 0.29). Conclusions: FES and FDG uptake in multiple lesions from ER+ male breast cancer patients did not differ from female breast cancer. Response and survival are also similar in male and female breast cancer patients in our study. Male breast cancer patients are appropriate for inclusion in imaging and clinical trials of endocrine and molecularly targeted therapies which are synergistic with endocrine therapy. Research Support: P01CA42045, R01CA72064, R01CA148131, DOD W81XWH-04-01-0675