Cancer

Internal medicine

PET-CT

Standardized uptake value

Positron emission tomography

Metastatic breast cancer

Endometrial cancer

Uterus

Endometrium

Nuclear medicine

Breast cancer

Medicine

European Journal of Nuclear Medicine and Molecular Imaging

Purpose 68 Ga-FAPI (fibroblast activation protein inhibitor) is a novel and highly promising radiotracer for PET/CT imaging. The aim of this retrospective analysis is to explore the potential of FAPI-PET/CT in gynecological malignancies. We assessed biodistribution, tumor uptake, and the influence of pre- or postmenopausal status on tracer accumulation in hormone-sensitive organs. Furthermore, a comparison with the current standard oncological tracer 18 F-FDG was performed in selected cases. Patients and methods A total of 31 patients (median age 59.5) from two centers with several gynecological tumors (breast cancer; ovarian cancer; cervical cancer; endometrial cancer; leiomyosarcoma of the uterus; tubal cancer) underwent 68 Ga-FAPI-PET/CT. Out of 31 patients, 10 received an additional 18 F-FDG scan within a median time interval of 12.5 days (range 1–76). Tracer uptake was quantified by standardized uptake values (SUV)max and (SUV)mean, and tumor-to-background ratio (TBR) was calculated (SUVmax tumor/ SUVmean organ). Moreover, a second cohort of 167 female patients with different malignancies was analyzed regarding their FAPI uptake in normal hormone-responsive organs: endometrium ( n = 128), ovary ( n = 64), and breast ( n = 147). These patients were categorized by age as premenopausal (&lt;35 years; n = 12), postmenopausal (&gt;65 years; n = 68), and unknown menstrual status (35–65 years; n = 87), followed by an analysis of FAPI uptake of the pre- and postmenopausal group. Results In 8 out of 31 patients, the primary tumor was present, and all 31 patients showed lesions suspicious for metastasis ( n = 81) demonstrating a high mean SUVmax in both the primary (SUVmax 11.6) and metastatic lesions (SUVmax 9.7). TBR was significantly higher in 68 Ga-FAPI compared to 18 F-FDG for distant metastases (13.0 vs. 5.7; p = 0.047) and by trend for regional lymph node metastases (31.9 vs 27.3; p = 0.6). Biodistribution of 68 Ga-FAPI-PET/CT presented significantly lower uptake or no significant differences in 15 out of 16 organs, compared to 18 F-FDG-PET/CT. The highest uptake of all primary lesions was obtained in endometrial carcinomas (mean SUVmax 18.4), followed by cervical carcinomas (mean SUVmax 15.22). In the second cohort, uptake in premenopausal patients differed significantly from postmenopausal patients in endometrium (11.7 vs 3.9; p &lt; 0.0001) and breast (1.8 vs 1.0; p = 0.004), whereas no significant difference concerning ovaries (2.8 vs 1.6; p = 0.141) was observed. Conclusion Due to high tracer uptake resulting in sharp contrasts in primary and metastatic lesions and higher TBRs than 18 F-FDG-PET/CT, 68 Ga-FAPI-PET/CT presents a promising imaging method for staging and follow-up of gynecological tumors. The presence or absence of the menstrual cycle seems to correlate with FAPI accumulation in the normal endometrium and breast. This first investigation of FAP ligands in gynecological tumor entities supports clinical application and further research in this field.

68Ga-FAPI-PET/CT in patients with various gynecological malignancies