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

Physiological Uptake of 68Ga-FAPI-04 in Female Reproductive System

PURPOSE

Since the avid uptake of 68Ga-labeled fibroblast activation protein inhibitor (68Ga-FAPI-04) observed in female reproductive organs, our objectives were to investigate the physiological uptake characteristics and provide preliminary reference ranges for clinical use.

PROCEDURES

We reviewed the findings of female patients who underwent 68Ga-FAPI-04 PET/CT at our institution between April 2022 and June 2023. The standard uptake value (SUV) of reproductive organs and menstrual information were collected. All patients were categorized into reproductive period group, perimenopause group, and postmenopause group. We analysed the uptake levels among the three groups, and their association with age and menstrual cycle.

RESULTS

A total of 109 patients were included in this study. Higher ovarian SUVs were detected in reproductive patients (SUVright: 2.75 ± 0.84, IQR: 1.39-5.26; SUVleft: 2.72, IQR: 2.34-3.20; p = 0.315) than in postmenopausal patients (SUVright: 2.27, IQR: 2.01-2.75; SUVleft: 2.38 ± 0.55, IQR: 1.35-3.60; p = 0.767), as well as uterine 68Ga-FAPI-04 accumulations. The SUVs of uterine fundus and corpus were approximately three times higher than that of the cervix. In reproductive period group, higher SUVs were observed in bilateral ovaries around the ovulatory phase to the early luteal phase, and higher uterine SUVs were noted in the menstrual and proliferative phases. The SUVs in all reproductive organs (except the ovaries) showed significant negative correlations with age in all patients (all p < 0.01).

CONCLUSIONS

68Ga-FAPI-04 SUVs in reproductive organs are higher in premenopausal patients than in postmenopausal patients. The 68Ga-FAPI-04 accumulation in reproductive organs might be associated with menstrual cycle. Including more patients from different menstrual phases could contribute to investigating the uptake characteristics and their underlying mechanisms.

99m Tc-HYNIC-FAPI-46 SPECT/CT Uptake in Lactating Breasts

ABSTRACT

A 36-year-old woman with a history of medullary thyroid carcinoma was referred for 99m Tc-HYNIC-FAPI-46 scan. Her calcitonin levels gradually increased after external beam radiation therapy, whereas her CEA levels were stable. A few suspicious tumoral lymphadenopathies were localized to the superior mediastinum. Interestingly, bilateral physiologic breast uptake was noticed, which was presumed to be due to lactation in the past 18 months. To our knowledge, physiologic breast uptake in 99m Tc-HYNIC-FAPI imaging has not been previously reported.