Increased 68Ga-FAPI Uptake in the Pulmonary Cryptococcus and the Postradiotherapy Inflammation

Differentiating lung neuroendocrine neoplasms from tumor-like infection using CT in patients with ectopic ACTH syndrome

OBJECTIVES

Pulmonary neuroendocrine neoplasms (NENs) are the most frequent cause of ectopic adrenocorticotropic hormone syndrome (EAS); lung infection is common in EAS. An imaging finding of infection in EAS patients can mimic NENs. This retrospective study investigated EAS-associated pulmonary imaging indicators.

METHODS

Forty-five pulmonary NENs and 27 tumor-like infections from 59 EAS patients (45 NEN and 14 infection patients) were included. Clinical manifestations, CT features, 18F-FDG, or 68Ga-DOTATATE-PET/CT images and pathological results were collected.

RESULTS

High-sensitivity C-reactive protein (p < 0.001) and expectoration occurrence (p = 0.04) were higher, and finger oxygen saturation (p = 0.01) was lower in the infection group than the NENs group. Higher-grade NENs were underrepresented in our cohort. Pulmonary NENs were solitary primary tumors, 80% of which were peripheral tumors. Overlying vessel sign and airway involvement were more frequent in the NENs group (p < 0.001). Multifocal (p = 0.001) and peripheral (p = 0.02) lesions, cavity (p < 0.001), spiculation (p = 0.01), pleural retraction (p < 0.001), connection to pulmonary veins (p = 0.02), and distal atelectasis or inflammatory exudation (p = 0.001) were more frequent in the infection group. The median CT value increment between the non-contrast and arterial phases was significantly higher in NENs lesions (p < 0.001). Receiver operating characteristic curve analysis indicated a moderate predictive ability at 48.3 HU of delta CT value (sensitivity, 95.0%; specificity, 54.1%).

CONCLUSION

Chest CT scans are valuable for localizing and characterizing pulmonary lesions in rare EAS, thereby enabling prompt differential diagnosis and treatment. CRITICAL RELEVANCE STATEMENT: Thin-slice CT images are valuable for the localization and identification of pulmonary ectopic adrenocorticotropic hormone syndrome lesions, leading to prompt differential diagnosis and effective treatment.

KEY POINTS

Lung tumor-like infections can mimic neuroendocrine neoplasms (NENs) in ectopic adrenocorticotropic hormone syndrome (EAS) patients. NENs are solitary lesions, whereas infections are multiple peripheral pseudotumors each with identifying imaging findings. Typical CT signs aid in localization and creating an appropriate differential diagnosis.

Elevated 68 Ga-FAPI Activity in Klebsiella pneumoniae Invasion Syndrome

ABSTRACT

Klebsiella pneumoniae invasion syndrome is a rare disease associated with primary liver abscess and secondary extrahepatic infection. We report a case of K. pneumoniae invasion syndrome with elevated 68 Ga-FAPI uptake, mimicking malignancy with multiple metastases. Our case illustrated that K. pneumoniae invasion syndrome should be considered as a possible etiology when diagnosing multiple 68 Ga-FAPI-avid liver foci with metastatic lesions. Besides, PET/CT could be an integrated tool to search for systemic occult lesions in K. pneumoniae invasion syndrome.

68 Ga-FAPI and 18 F-FDG Uptake in a Patient With Esophageal Candida Infection

ABSTRACT

A 67-year-old woman presented with dysphagia for 2 months. Enhanced chest CT suggested thickening of the esophageal wall, which was suspected to be a malignancy. The patient then underwent 18 F-FDG and 68 Ga-FAPI PET/CT. Increased uptake was observed in both tracers in the thickened esophageal wall. However, biopsy demonstrated candida infection of esophagus. After treatment, the symptoms of the patient were relieved.

Elevated 68 Ga-FAPI-04 Activity Due to Staphylococcus aureus Intracranial Infection

ABSTRACT

A 37-year-old man was admitted to our hospital after experiencing syncope. An MRI of his head revealed multiple foci of abnormal signal, which could potentially be metastases. The patient then underwent a 68 Ga-FAPI-04 PET/MRI examination, which revealed multiple FAPI-avid foci in the brain. Upon analyzing the cerebrospinal fluid, it was found that the patient had a Staphylococcus aureus infection. The results suggest that 68 Ga-FAPI-04 PET has the potential to be a valuable tool in the visualization of intracranial infectious lesions.

Pulmonary Cryptococcosis: Intense Uptake on Both 18 F-FDG and 68 Ga-FAPI PET/CT

ABSTRACT

A 57-year-old woman without hepatitis B or immunodeficiency presented with right upper abdominal pain and cough for 3 months. CT revealed one nodule in the lung and another in the liver. Both 18 F-FDG and 68 Ga-FAPI PET/CT showed increased tracer uptake in these 2 nodules, suggesting pulmonary carcinoma with hepatic metastasis. Finally, biopsies of these 2 nodules demonstrated the diagnoses of hepatic adenocarcinoma and pulmonary cryptococcosis. This case highlights that cryptococcosis can be FAPI-avid.

Increased 68 Ga-FAPI Uptake in Pulmonary Sclerosing Pneumocytoma

ABSTRACT

Pulmonary sclerosing pneumocytoma is a rare benign neoplasm arising from the primitive respiratory epithelium. Here, we report 68 Ga-FAPI PET/CT findings of pulmonary sclerosing pneumocytoma in a 55-year-old woman. The images showed a solitary pulmonary mass in the left lower lobe with intense 68 Ga-FAPI uptake. Our case illustrates that the sclerosing pneumocytoma should be taken into consideration as one of the differential diagnoses in lung nodules/masses with intense 68 Ga-FAPI uptake.

Increased FAPI Activity in Pulmonary Tuberculosis

ABSTRACT

A 50-year-old man presented with cough and hemoptysis for 1 month. Chest CT showed an irregular mass in the right lung, with enlarged lymph nodes in the mediastinum and right hilum. These findings were suggestive of lung cancer with lymph node metastases. The patient was subsequently enrolled in a 68Ga-DOTA-FAPI-04 PET/CT clinical trial. 68Ga-DOTA-FAPI-04 PET/CT revealed a mass in the upper lobe of right lung, with intense tracer uptake. Meanwhile, PET/CT showed enlarged lymph nodes in the mediastinum and right hilum, with mild FAPI uptake. However, pathological examination confirmed the mass was tuberculous granuloma.

Non-oncologic incidental uptake on FAPI PET/CT imaging

Fibroblast-activation protein (FAP) is a serine protease classified in the dipeptidyl peptidase 4 (DPP4) family. FAP is predominantly expressed in activated fibroblasts such as the cancer-associated fibroblasts (CAFs). FAP expression in CAFs is associated with tumor progression and poor prognosis in solid cancers. Recently, radiolabeled FAP inhibitors (FAPI) has been developed, which enables positron emission tomography (PET) imaging of FAP. FAPI PET/CT can provide a higher tumor-to-background ratio (TBR) than 18F-fludeoxyglucose PET/CT in various cancers, and thus has attracted substantial attention. As studies on FAPI PET grow in number and size, incidental findings related to non-oncologic conditions have been increasingly reported. FAPI PET uptake has been reported in various conditions such as benign tumors, fibrotic, granulomatosis, scarring/wound, degenerative diseases, and inflammatory diseases.The knowledge of physiological and non-oncologic causes of FAPI uptake is indispensable for accurate FAPI PET/CT interpretation and can help appropriate management of incidental findings on FAPI PET/CT in patients referred for cancer staging indications. In this review article, we describe for each organ system (Brain, Oral mucosa, Salivary Glands, Thyroid, Lung, Myocardium, Breast, Esophagus, Stomach, Intestine, Liver, Gallbladder, Pancreas, Spleen, Kidney, , Uterus, Bone marrow, Joints, Muscle, Vessels, Lymph nodes), the patterns of physiological FAPI uptake and the main causes of non-oncological uptake reported from the literature with FAPI-02, FAPI-04 and FAPI-46. We also illustrate some examples from our institutional database at UCLA.

Enhancing Clinical Diagnosis for Patients With Persistent Pulmonary Abnormalities After COVID-19 Infection: The Potential Benefit of 68 Ga-FAPI PET/CT

PATIENTS AND METHODS

Six post COVID-19 patients suspected for pulmonary fibrosis were scheduled for dual-tracer PET/CT with 18 F-FDG and 68 Ga-fibroblast activation protein inhibitor (FAPI)-46. The uptake of 68 Ga-FAPI-46 in the involved lung was compared with a control group of 9 non-COVID-19 patients. Clinical data and PET/CT imaging were collected and analyzed.

RESULTS

PET/CT revealed in all 6 pulmonary impaired patients the reduced glucose avidity on 18 F-FDG and clear positivity on 68 Ga-FAPI-46 PET/CT in comparison to the control group.

CONCLUSIONS

Enhancing fibrotic repair mechanisms, 68 Ga-FAPI PET/CT may improve noninvasive clinical diagnostic performance in patients with long-term CT abnormalities after severe COVID-19. Although this study shows promising results, additional studies in larger populations are required to establish a general diagnostic guideline.

Positron emission tomography and computed tomography with [68Ga]Ga-fibroblast activation protein inhibitors improves tumor detection and staging in patients with pancreatic cancer

PURPOSE

This study aimed to investigate the diagnostic performance of [68Ga]Ga-FAPI PET/CT for primary and metastatic pancreatic carcinoma lesions and compare the results with those of [18F]-fluorodeoxyglucose ([18F]FDG) PET/CT.

METHODS

Patients with suspected or diagnosed pancreatic malignancy, who underwent contemporaneous [18F]FDG and [68Ga]Ga-FAPI PET/CT between June 2020 and January 2021, were retrospectively analyzed. Routine contrast-enhanced CT (CE-CT) is performed in all patients as standardized care. Findings were confirmed by histopathology or radiographic follow-up. We compared radiotracer uptake, diagnostic performance, and TNM (tumor-node-metastasis) classifications.

RESULTS

We evaluated 36 participants (25/36 men; median age, 60 years), including 26 patients with pancreatic malignancies and ten patients with pancreatic benign lesions. [68Ga]Ga-FAPI PET/CT showed higher radiotracer uptake and higher sensitivity than [18F]FDG PET/CT in evaluating primary tumors (SUVmax, 21.4 vs. 4.8; sensitivity, 100% vs. 73.1%), involved lymph nodes (SUVmax, 8.6 vs. 2.7; sensitivity, 81.8% vs. 59.1%), and metastases (SUVmax, 7.9 vs. 3.5; sensitivity, 91.5% vs. 44.0%); Compared with [18F]FDG, [68Ga]Ga-FAPI PET/CT upstaged six patients' TNM staging (6/23, 26.1%) and changed two patients' clinical management (2/23, 8.7%). Compared with CE-CT, [68Ga]Ga-FAPI PET/CT upgraded TNM staging in five patients (5/23, 21.7%) and changed the therapeutic regimen in only one patient (1/23, 4.3%). Intense [68Ga]Ga-FAPI uptake was observed throughout the pancreas in 12/26 pancreatic malignancies; dual-time point [68Ga]Ga-FAPI PET/CT may differentiate pancreatitis from malignancy.

CONCLUSIONS

Compared with [18F]FDG PET/CT, [68Ga]Ga-FAPI PET/CT shows higher sensitivity in detecting primary pancreatic tumors, involved lymph nodes, and metastases and is superior in terms of TNM staging. Prospective trials with larger patient population are needed to evaluate whether [68Ga]Ga-FAPI PET/CT could elicit treatment modification in pancreatic cancer when compared with standard of care imaging.