Physiological Uptake Characteristics of Breast on 68Ga-FAPI-04 PET/CT.

Abstract

Gallium 68 (68Ga)-labeled fibroblast activation protein inhibitor (FAPI) PET/CT is sensitive on breast cancer staging, but its clinical utility may be limited by the high physiological 68Ga-FAPI-04 uptake in normal breast tissue that can obscure primary tumors. The aim of this study was to elucidate the characteristics of physiological 68Ga-FAPI-04 uptake in normal breast. A total of 143 consecutive women with 68Ga-FAPI-04 PET/CT data were reviewed retrospectively. SUVmax, density and thickness of breast, as well as SUVmax of nipple, were measured. Univariate and multivariate regression analyses were used to identify factors related to the breast and nipple SUVs. Twenty-eight premenopausal, 62 menopausal and 10 post-operative (after bilateral adnexectomy) women with 103 examinations were included. All had a diffuse, symmetrical uptake in breast. There was no difference in 68Ga-FAPI-04 uptake between bilateral breasts (right: median, 1.14[IQR, 0.85-1.54] vs. left: median, 1.09[IQR, 0.86-1.54]; P = 0.253). Patients in menstrual status with expected high estrogen level (late follicular, ovulatory and mid luteal phases) had higher breast SUVs (median SUV, 3.91 [IQR, 2.85-4.35]) than those with expected moderate (early follicular, early luteal and late luteal phases; median SUV, 1.57 [IQR, 1.39-2.08]; P < 0.001) or low level (menopause and post-operation; median SUV, 0.98 [IQR, 0.83-1.21]; P < 0.001). Menstrual status was an independent predictors of breast SUV (r2 = 0.689, P < 0.001). All the patients had a focal, symmetrical uptake in nipples. Nipple SUV did not correlate with menstrual status (P = 0.913).