Comparison of physiological uptake of normal tissues in patients with cancer using 18F-FAPI-04 and 18F-FAPI-42 PET/CT

Impact of fat intake on [18F]AlF-NOTA-FAPI-04 uptake in normal abdominal organs

Purpose

[18F]AlF-NOTA-FAPI-04 demonstrates significant physiological uptake in the gallbladder and biliary tract system, representing a limitation of this positron emission tomography (PET) tracer. The aim of this study was to evaluate the impact of milk consumed prior to a PET/CT scan on [18F]AlF-NOTA-FAPI-04 uptake in normal abdominal organs.

Materials and methods

A total of 86 patients who underwent [18F]AlF-NOTA-FAPI-04 PET/CT imaging took part in this single-center retrospective clinical study at the Hunan Cancer Hospital between December 2020 and August 2021. Patients were divided into two groups according to their pre-PET scan diet: treated group, who consumed 250 mL of milk 10 ± 5 min after the tracer injection, while the control group was permitted no food intake subsequent to the radiotracer administration. The mean standardized uptake value (SUVmean) of gallbladder, liver, small intestine and pancreas were measured in 18F-FAPI and 18F-FDG PET/CT.

Results

There was a statistically significant difference in the 18F-FAPI uptake in the gallbladder between the treated group and the control group (p < 0.001). The average SUVmean in the treated group was 2.19 ± 2.01, which was significantly lower than the average SUVmean of 10.04 ± 9.66 in the control group. In the subgroup analysis of patients who underwent paired [18F]FDG and [18F]FAPI PET/CT scans, the 18F-FAPI uptake of liver and small intestine was significantly lower than the 18F-FDG uptake in both the treated group and the control group (p < 0.001).

Conclusion

This study suggests that milk consumption decreases physiological 18F-FAPI uptake in the gallbladder, potentially enhancing the diagnostic accuracy for gallbladder cancer.

Tumor microenvironment and fibroblast activation protein inhibitor (FAPI) PET: developments toward brain imaging

Fibroblast activation protein (FAP) is a type-II membrane bound glycoprotein specifically expressed by activated fibroblasts almost exclusively in pathological conditions including arthritis, fibrosis and cancer. FAP is overexpressed in cancer-associated fibroblasts (CAFs) located in tumor stroma, and is known to be involved in a variety of tumor-promoting activities such as angiogenesis, proliferation, resistance to chemotherapy, extracellular matrix remodeling and immunosuppression. In most cancer types, higher FAP expression is associated with worse clinical outcomes, leading to the hypothesis that FAP activity is involved in cancer development, cancer cell migration, and cancer spread. Recently, various high selectivity FAP inhibitors (FAPIs) have been developed and subsequently used for positron emission tomography (PET) imaging of different pathologies. Considering the paucity of widely available and especially mainstream reliable radioligands in brain cancer PET imaging, and the poor survival rates of patients with certain types of brain cancer such as glioblastoma, FAPI-PET represents a major development in enabling the detection of small primary or metastatic lesions in the brain due to its biological characteristics and low background accumulation. In this work, we aim to summarize the potential avenues for use of FAPI-PET, from the basic biological processes to oncologic imaging and with a main focus on brain imaging.

Non-tumoral uptake of 68Ga-FAPI-04 PET: A retrospective study

OBJECTIVE

Fibroblast activation protein (FAP)-targeting radiopharmaceutical based on the FAP-specific inhibitor (FAPI) is considered as a potential alternative agent to FDG for tumor-specific imaging. However, FAP is also expressed in normal adult tissues. The aim of this study was to explore the image features of non-tumoral regions with high uptake of ⁶⁸Ga-FAPI-04 in positron emission tomography (PET) imaging and to reveal the physiological mechanisms of these regions.

MATERIAL

A total of 137 patients who underwent whole-body ⁶⁸Ga-FAPI-04 PET/MR (n=46) or PET/CT (n=91) were included in this retrospective study. Three experienced nuclear medicine physicians determined the non-tumoral regions according to other imaging modalities (CT, MRI, ¹⁸F-FDG PET, or ultrasound), clinical information, or pathological results. The regions of interest (ROIs) were drawn manually, and the maximum standardized uptake value (SUV_max) was measured.

RESULTS

A total of 392 non-tumoral uptake regions were included in this study. The included physiological regions were uterus (n=38), submandibular gland (n=118), nipple (n=37), gingiva (n=65), and esophagus (n=31). The incidence of ⁶⁸Ga-FAPI-04 uptake in physiological regions was independent of age, the tracer uptakes in the gingiva and esophagus were more common in male patients (p=0.006, 0.009), while that in the nipple was more common in female patients (p < 0.001). The included benign regions were inflammatory lymph node (n =10), pneumonia (n=13), atherosclerosis (n=10), pancreatitis (n=18), osteosclerosis (n=45), and surgical scar (n=7). No significant difference was observed in SUV_max between physiological and benign regions.

CONCLUSIONS

A number of organs exhibit physiological uptakes of ⁶⁸Ga-FAPI-04. Our study showed that regions with high ⁶⁸Ga-FAPI-04 uptake did not necessarily represent malignancy. Being familiar with physiological and typical benign ⁶⁸Ga-FAPI-04 uptake regions can be helpful for physicians to interpret images and to make an accurate diagnosis.