Head-to-head comparison of [18F]-FDG and [68 Ga]-DOTA-FAPI-04 PET/CT for radiological evaluation of platinum-sensitive recurrent ovarian cancer

Comparison of 68Ga-FAPI-04 and 18F-FDG PET/CT in diagnosing ovarian cancer

PURPOSE

This study assesses the diagnostic performance of 68Ga-FAPI-04 PET/CT compared to 18F-FDG PET/CT in primary, recurrent, and metastatic ovarian cancer.

METHODS

Seventy-nine ovarian cancer patients who performed 68Ga-FAPI-04 and 18F-FDG PET/CT were recruited. The target-to-background ratio (TBR), maximum standardized uptake value (SUVmax), the number of positive lesions, visual assessment, the peritoneal cancer index (PCI) score, staging/restaging, and treatment strategies were compared from the corresponding PET/CT. Additionally, we analyzed and contrasted the diagnostic efficacy in both scans.

RESULTS

Among all patients, 6 were assessed for initial assessment and 73 for recurrence and metastasis detection. For all lesions, 68Ga-FAPI-04 PET/CT demonstrated greater TBR than 18F-FDG PET/CT. 68Ga-FAPI-04 PET/CT demonstrated higher sensitivity for peritoneal metastases including patient-based and lesion-based analysis (95.00% vs. 83.33%, P = 0.065; 90.16% vs. 60.66%, P < 0.001) and a higher PCI score [median PCI: 6 (4, 12) vs. 4 (2, 8), P < 0.001]. According to the visual assessment, 68Ga-FAPI-04 PET revealed larger extent metastases in 55.93% (33/59) of the patients with peritoneal metastases. 68Ga-FAPI-04 was upstaged in 7 patients (8.86%, 7/79) and discrepancies in both scans caused treatment strategies to change in 11 patients (13.92%, 11/79).

CONCLUSION

68Ga-FAPI-04 PET/CT outperforms 18F-FDG PET/CT in identifying metastases and can be a potential supplement for managing ovarian cancer patients.

Diagnostic accuracy and clinical value of [68Ga]Ga-FAPI-46 PET/CT for staging patients with ovarian cancer: study protocol for a prospective clinical trial

BACKGROUND

[18F]Fluorodeoxyglucose ([18F]FDG) positron emission tomography (PET) is recommended during diagnostic work-up for ovarian cancer; however, [18F]FDG PET has several inherent limitations. The novel oncologic PET-tracer fibroblast activation protein inhibitor (FAPI) has demonstrated promising results in multiple cancer types, including ovarian cancer, and could overcome the limitations of [18F]FDG PET; however, high-quality clinical studies are lacking. The primary objective of the present study is to compare the diagnostic accuracy of [68Ga]Ga-FAPI-46 PET/CT and [18F]FDG PET/CT in ovarian cancer patients and to investigate how this potential difference impacts staging and patient management.

METHODS AND DESIGN

Fifty consecutive ovarian cancer patients will be recruited from Aalborg University Hospital, Denmark. This study will be a single-center, prospective, exploratory clinical trial that adheres to the standards for reporting diagnostic accuracy studies (STARD). This study will be conducted under continuous Good Clinical Practice monitoring. The eligibility criteria for patients are as follows: (1) biopsy verified newly diagnosed ovarian cancer or a high risk of ovarian cancer and referred for primary staging with [18F]FDG PET/CT; and (2) resectable disease, i.e., candidate for primary debulking surgery or neoadjuvant chemotherapy followed by interval debulking surgery. All recruited study subjects will undergo [68Ga]Ga-FAPI-46 PET/CT at primary staging, before primary debulking surgery or neoadjuvant chemotherapy (Group A + B), in addition to conventional imaging (including [18F]FDG PET/CT). Study subjects in Group B will undergo an additional [68Ga]Ga-FAPI-46 PET/CT following neoadjuvant chemotherapy prior to interval debulking surgery. The results of the study-related [68Ga]Ga-FAPI-46 PET/CTs will be blinded, and treatment allocation will be based on common clinical practice in accordance with current guidelines. The histopathology of surgical specimens will serve as a reference standard. A recruitment period of 2 years is estimated; the trial is currently recruiting.

DISCUSSION

To our knowledge, this trial represents the largest, most extensive, and most meticulous prospective FAPI PET study conducted in patients with ovarian cancer thus far. This study aims to obtain a reliable estimation of the diagnostic accuracy of [68Ga]Ga-FAPI-46 PET/CT, shed light on the clinical importance of [68Ga]Ga-FAPI-46 PET/CT, and examine the potential applicability of [68Ga]Ga-FAPI-46 PET/CT for evaluating chemotherapy response.

TRIAL REGISTRATION

clinicaltrials.gov: NCT05903807, 2nd June 2023; and euclinicaltrials.eu EU CT Number: 2023-505938-98-00, authorized 11th September 2023.

Surgical evidence-based comparison of [68Ga]Ga-FAPI-04 PET and MRI-DWI for assisting debulking surgery in ovarian cancer patients

PURPOSE

Imaging assessment of abdominopelvic tumor burden is crucial for debulking surgery decision in ovarian cancer patients. This study aims to compare the efficiency of [68Ga]Ga-FAPI-04 FAPI PET and MRI-DWI in the preoperative evaluation and its potential impact to debulking surgery decision.

METHODS

Thirty-six patients with suspected/confirmed ovarian cancer were enrolled and underwent integrated [68Ga]Ga-FAPI-04 PET/MRI. Nineteen patients (15 stage III-IV and 4 I-II stage) who underwent debulking surgery were involved in the diagnostic efficiency analysis. The images of [68Ga]Ga-FAPI-04 PET and MRI-DWI were visually analyzed respectively. Immunohistochemistry on FAP was performed in metastatic lesions to investigate the radiological missing of [68Ga]Ga-FAPI-04 PET as well as its different performance in primary debulking surgery (PDS) and interval debulking surgery (IDS) patients. Potential imaging impact on management was also studied in 35 confirmed ovarian cancer patients.

RESULTS

[68Ga]Ga-FAPI-04 PET displayed higher sensitivity (76.8% vs.59.9%), higher accuracy (84.9% vs. 80.7%), and lower missing rate (23.2% vs. 40.1%) than MRI-DWI in detecting abdominopelvic metastasis. The diagnostic superiority of [68Ga]Ga-FAPI-04 PET is more obvious in PDS patients but diminished in IDS patients. [68Ga]Ga-FAPI-04 PET outperformed MRI-DWI in 70.8% abdominopelvic regions (17/24), which contained seven key regions that impact the resectability and surgical complexity. MRI-DWI hold advantage in the peritoneal surface of the bladder and the central tendon of the diaphragm. Of the contradictory judgments between the two modalities (14.9%), [68Ga]Ga-FAPI-04 PET correctly identified more lesions, particularly in PDS patients (73.8%). In addition, FAP expression was independent of lesion size and decreased in IDS patients. [68Ga]Ga-FAPI-04 PET changed 42% of surgical planning that was previously based on MRI-DWI.

CONCLUSION

[68Ga]Ga-FAPI-04 PET is more efficient in assisting debulking surgery in ovarian cancer patients than MRI-DWI. Integrated [68Ga]Ga-FAPI-04 PET/MR imaging is a potential method for planning debulking surgery in ovarian cancer patients.

Applications of FAPI PET/CT in the diagnosis and treatment of breast and the most common gynecologic malignancies: a literature review

The fibroblast activating protein (FAP) is expressed by some fibroblasts found in healthy tissues. However, FAP is overexpressed in more than 90% of epithelial tumors, including breast and gynecological tumors. As a result, the FAP ligand could be used as a target for diagnosis and treatment purposes. Positron emission tomography/computed tomography (PET/CT) is a hybrid imaging technique commonly used to locate and assess the tumor's molecular and metabolic functions. PET imaging involves the injection of a radiotracer that tends to accumulate more in metabolically active lesions such as cancer. Several radiotracers have been developed to target FAP in PET/CT imaging, such as the fibroblast-activation protein inhibitor (FAPI). These tracers bind to FAP with high specificity and affinity, allowing for the non-invasive detection and quantification of FAP expression in tumors. In this review, we discussed the applications of FAPI PET/CT in the diagnosis and treatment of breast and the most common gynecologic malignancies. Radiolabeled FAPI can improve the detection, staging, and assessment of treatment response in breast and the most common gynecologic malignancies, but the problem with normal hormone-responsive organs remains insurmountable. Compared to the diagnostic applications of FAPI, further research is needed for future therapeutic applications.

Feasibility of One-Day PET/CT Scanning Protocol with 68Ga-DOTA-FAPI-04 and 18F-FDG for the Detection of Ovarian Cancer Recurrence and Metastasis

Objective: The objective of this study was to investigate the feasibility of 1-d 68Ga-DOTA-FAPI-04 and 18F-FDG (2-deoxy-2[18F]fluoro-d-glucose) positron emission tomography/computed tomography (PET/CT) for detecting ovarian cancer recurrence and metastasis. Materials and Methods: Fifty-two patients who underwent 18F-FDG and 68Ga-DOTA-FAPI-04 PET/CT were divided into 1- and 2-d groups. Image acquisition, injection time, and total waiting time were compared. For the 68Ga-DOTA-FAPI-04 PET/CT scans, low-dose CT scans and low injection dosages were employed, and total radiation dose was assessed for both protocols. The comparative analysis included assessment of patient-based detection rates and lesion-based diagnostic efficacy. Results: The total waiting time was significantly shorter in the 1-d group than in the 2-d group (p = 0.000). The radiation doses stemming from internal radiation and external radiation between the groups showed no differences (p = 0.151 vs. 0.716). In the patient-based analysis, the detection rates for local recurrence, peritoneal, lymph node, and other metastases were not significantly different in both protocols (p ∈ [0.351, 1.000]). For the lesion-based analysis, no differences were noted in terms of sensitivity, specificity, positive predictive value, negative predictive value, and accuracy (p ∈ [0.371, 1.000]). Conclusions: The 1-d PET/CT protocol reduced waiting time and exhibited equivalent detectability compared with the 2-d protocol, suggesting its clinical value.

Imaging Evaluation of Peritoneal Metastasis: Current and Promising Techniques

Early diagnosis, accurate assessment, and localization of peritoneal metastasis (PM) are essential for the selection of appropriate treatments and surgical guidance. However, available imaging modalities (computed tomography [CT], conventional magnetic resonance imaging [MRI], and 18fluorodeoxyglucose positron emission tomography [PET]/CT) have limitations. The advent of new imaging techniques and novel molecular imaging agents have revealed molecular processes in the tumor microenvironment as an application for the early diagnosis and assessment of PM as well as real-time guided surgical resection, which has changed clinical management. In contrast to clinical imaging, which is purely qualitative and subjective for interpreting macroscopic structures, radiomics and artificial intelligence (AI) capitalize on high-dimensional numerical data from images that may reflect tumor pathophysiology. A predictive model can be used to predict the occurrence, recurrence, and prognosis of PM, thereby avoiding unnecessary exploratory surgeries. This review summarizes the role and status of different imaging techniques, especially new imaging strategies such as spectral photon-counting CT, fibroblast activation protein inhibitor (FAPI) PET/CT, near-infrared fluorescence imaging, and PET/MRI, for early diagnosis, assessment of surgical indications, and recurrence monitoring in patients with PM. The clinical applications, limitations, and solutions for fluorescence imaging, radiomics, and AI are also discussed.

[68Ga]Ga-FAPI-04 PET/CT in the evaluation of epithelial ovarian cancer: comparison with [18F]F-FDG PET/CT

PURPOSE

To compare the efficacy of [68Ga]Ga-FAPI-04 PET/CT in primary or recurrent tumors and metastatic lesions of epithelial ovarian cancer (EOC) with that of fluorine-18 fluorodeoxyglucose ([18F]F-FDG) PET/CT.

METHODS

Forty-nine patients (median age, 57 years; IQR, 51-66 years) with histologically proven primary or relapsed EOC were enrolled. Participants underwent [18F]F-FDG and [68Ga]Ga-FAPI-04 PET/CT. The detection rate, diagnostic accuracy, semiquantitative parameters, tumor staging, and clinical management of the tracers were compared. The diagnostic performance of [18F]F-FDG and [68Ga]Ga-FAPI-04 PET/CT was evaluated and compared using surgical pathology. Differences between methods regarding the peritoneal cancer index (PCI) using preoperative imaging, surgical PCI, and tumor markers (CA125, HE4) were also assessed regarding peritoneal metastases.

RESULTS

Among the 49 patients, 28 had primary EOC; 21 had relapsed EOC. [68Ga]Ga-FAPI-04 PET/CT outperformed [18F]F-FDG PET/CT in detecting peritoneal metastases (96.8% vs. 83.0%; p < 0.001), retroperitoneal (99.5% vs. 91.4%; p < 0.001), and supradiaphragmatic lymph node metastases (100% vs. 80.4%; p < 0.001). Compared with [18F]F-FDG, [68Ga]Ga-FAPI-04 showed higher SUVmax for peritoneal metastases (17.31 vs. 13.68; p = 0.026) and retroperitoneal (8.72 vs. 6.56; p < 0.001) and supradiaphragmatic lymph node metastases (6.39 vs. 4.20; p < 0.001). Moreover, [68Ga]Ga-FAPI-04 PET/CT showed higher sensitivity compared with [18F]F-FDG PET/CT for detecting metastatic lymph nodes (80.6% vs. 61.3%; p = 0.031) and peritoneal metastases (97.5% vs. 75.9%; p < 0.001), using surgical pathology as the gold standard. Compared with [18F]F-FDG PET/CT, [68Ga]Ga-FAPI-04 PET/CT led to an upgrade in 14.3% and 33.3% of treatment-naive and relapse participants, resulting in management changes in 10.7% and 19.0% of the patients, respectively. The median PCIFAPI scores were significantly higher than PCIFDG (15 vs. 11; p < 0.001) and positively correlated with CA125 and HE4 levels and surgical PCI.

CONCLUSION

[68Ga]Ga-FAPI-04 PET/CT achieved higher sensitivity than [18F]F-FDG PET/CT in the detection and diagnosis of lymph node and peritoneal metastases, suggesting advantages regarding the preoperative staging of patients with EOC and, thereby, improving treatment decision-making.

TRIAL REGISTRATION

NCT05034146. Registered February 23, 2021.

Head-to-Head Comparison of FDG and Radiolabeled FAPI PET: A Systematic Review of the Literature

FAPI-based radiopharmaceuticals are a novel class of tracers, mainly used for PET imaging, which have demonstrated several advantages over [18F]FDG, especially in the case of low-grade or well-differentiated tumors. We conducted this systematic review to evaluate all the studies where a head-to-head comparison had been performed to explore the potential utility of FAPI tracers in clinical practice. FAPI-based radiopharmaceuticals have shown promising results globally, in particular in detecting peritoneal carcinomatosis, but studies with wider populations are needed to better understand all the advantages of these new radiopharmaceuticals.

Correlation between [68Ga]Ga-FAPI-46 PET Imaging and HIF-1α Immunohistochemical Analysis in Cervical Cancer: Proof-of-Concept

Hypoxia leads to changes in tumor microenvironment (upregulated CAFs) with resultant aggressiveness. A key factor in the physiological response to hypoxia is hypoxia-inducible factor-1alpha (HIF-1α). [68Ga]Ga-FAPI PET imaging has been demonstrated in various cancer types. We hypothesized that [68Ga]Ga-FAPI PET may be used as an indirect tracer for mapping hypoxia by correlating the image findings to pathological analysis of HIF-1α expression. The [68Ga]Ga-FAPI PET/CT scans of women with cancer of the cervix were reviewed and the maximum and mean standardized uptake value (SUVmax and SUVmean) and FAPI tumor volume (FAPI-TV) were documented. Correlation analysis was performed between PET-derived parameters and immunohistochemical staining as well as between PET-derived parameters and the presence of metastasis. Ten women were included. All patients demonstrated tracer uptake in the primary site or region of the primary. All patients had lymph node metastases while only six patients had distant visceral or skeletal metastases. The mean SUVmax, SUVmean, and FAPI-TV was 18.89, 6.88, and 195.66 cm3, respectively. The average FAPI-TV for patients with additional sites of metastases was higher than those without. Immunohistochemistry revealed varying intensities of HIF-1α expression in all tested samples. There was a positive correlation between the presence of skeletal metastases and staining for HIF-1α (r=0.80;p=0.017). The presence of skeletal metastasis was correlated to the HIF-1⍺ staining (percentage distribution). Furthermore, the FAPI-TV was a better predictor of metastatic disease than the SUVmax.