68Ga-Labeled Fibroblast Activation Protein Inhibitor PET/CT for the Early and Late Prediction of Pathologic Response to Neoadjuvant Chemotherapy in Breast Cancer Patients: A Prospective Study

Revolutionizing cancer diagnosis and dose biodistribution: a meta-analysis of [68ga] FAPI- 46 vs. [18f] FDG imaging

BACKGROUND

Advancements in novel peptides significantly affect cancer diagnosis by targeting cancer-specific markers, thereby improving imaging modalities, such as positron emission tomography combined with computed tomography (PET/CT) for more accurate tumor detection. This systematic review and meta-analysis aimed to assess the diagnostic accuracy of [18F] Fluorodeoxyglucose (FDG) and 68Ga-fibroblast activation protein inhibitor (FAPI- 46) PET/CT for early cancer detection.

METHODS

A comprehensive search was conducted in Scopus, MEDLINE, Web of Science, and Embase databases up to March 28, 2024, using MeSH keywords. Titles and abstracts were screened to identify studies on hybrid [68Ga] FAPI- 46 and [18F] FDG, followed by a detailed full-text evaluation. Only cohort or cross-sectional studies published in English, focusing on the clinical diagnosis of cancer patients, were included, while reviews, case reports, conference proceedings, and abstracts were excluded. Random-effects meta-analysis was used for the estimation of pooled specificity and sensitivity with 95% confidence intervals (CIs). In addition, the heterogeneity was assessed across studies and subgroup meta-analyses for the detection rate via Stata.

RESULTS

Among the 615 retrieved studies, nine articles were incorporated in the present systematic review, with five (n = 144 patients) eligible for meta-analysis. For [68Ga] FAPI- 46, the pooled sensitivity and specificity compared with immunohistopathology were 0.96 (95% CI 0.84, 0.99) and 0.92 (95% CI 0.53, 0.99), respectively, with a positive likelihood ratio (LR +) of 4.41 (95% CI 1.64, 11.79) and a negative likelihood ratio (LR -) of 3.07 (95% CI 1.01, 9.37). For [18F] FDG, pooled sensitivity and specificity compared with immunohistopathology were 0.73 (95% CI 0.34, 0.93) and 0.83 (95% CI 0.57, 0.95), with an LR + of 12.73 (95% CI 1.43, 113.45) and an LR - of 0.32 (95% CI 0.11, 0.17). The pooled odds ratio for the detection rate on a per-lesion basis was 1.73 (95% CI 0.99, 3.02) for [68Ga] FAPI- 46 compared with [18F] FDG. The pooled weighted mean differences in the standardized uptake value (SUVmax) for primary tumor uptake and the tumor-to-background ratio (TBR) in [68Ga] FAPI- 46 vs. 18F-FDG were 4.40 (95% CI - 0.7, 9.5) and 6.18 (95% CI 1.74, 10.61), respectively. Moderate to high heterogeneity was noted because of the variations in patient selection, interpretation criteria, and scanning procedures.

CONCLUSIONS

This study revealed that [68Ga] FAPI- 46 outperforms [18F] FDG in cancer diagnosis, with higher sensitivity (0.96 vs. 0.73) and specificity (0.92 vs. 0.83). [Ga] FAPI- 46 improved tumor detection with higher SUVmax and TBR. While FDG had a higher LR +, its lower LR - highlighted more false negatives. Accordingly, [68Ga] FAPI- 46 exhibited superior accuracy and reliability than FDG in cancer diagnosis.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD 42023472270.

FAPI radiopharmaceuticals in nuclear oncology and theranostics of solid tumours: are we nearer to surrounding the hallmarks of cancer?

[18F]FDG PET/CT is the most widely used PET radiopharmaceutical in oncology, but it is not exempt of diagnostic limitations. FAPI have emerged as a great tool in the management of several different solid tumours in which [18F]FDG is not able to provide enough information. The aim of this work was to evaluate the available evidence on diagnostic and therapeutic applications of PET/CT with FAPI radiopharmaceuticals. We underwent a non-systematic review focusing in the utility of FAPI radiopharmaceuticals in PET/CT diagnosis and in the treatment of several malignancies. FAPI radiopharmaceuticals present characteristics that can potentially overcome some known diagnostic limitations of [18F]FDG. FAPI radiopharmaceuticals present a high target-to-background ratio (TBR) in many solid tumours such as oesophageal cancer, gastric cancer, pancreatic cancer, hepatic cancer, colorectal cancer, breast cancer, ovarian, cervical cancer, and head and neck cancer. Available evidence suggests the high TBR improves sensitivity and specificity compared to [18F]FDG, especially for the detection of lymphadenopathies and peritoneal metastases, and may improve patient management and radiation treatment planning. Moreover, it is important to underline the potential theranostic application of FAPI radiopharmaceuticals.

Fibroblast Activation Protein Inhibitor (FAPI)-Based Theranostics

Fibroblast activation protein (FAP) is a serine protease selectively expressed in cancer-associated fibroblasts (CAFs), fibrotic tissues, and areas of active tissue remodeling, making it an attractive target for diagnostic imaging across a spectrum of disease. FAP inhibitors (FAPIs) labeled with PET tracers have rapidly advanced as a novel imaging modality with broad clinical applications that offers several advantages, including rapid tumor accumulation, low background uptake, and high tumor-to-background ratios. In oncology, FAPI PET has demonstrated excellent performance in visualizing a wide range of malignancies, including those with low glycolytic activity, such as pancreatic cancer, cholangiocarcinoma, and certain sarcomas. Its high sensitivity and specificity for the stromal component enables improved tumor delineation, staging, and response assessment. Additionally, the potential to guide theranostic approaches, where the same tracer can be labeled with therapeutic radionuclides, positions FAPI as a key player in precision oncology. Beyond oncology, FAPI PET has shown promise in imaging conditions characterized by fibrotic and inflammatory processes. In the cardiovascular field, FAPI PET imaging is being investigated for its ability to detect myocardial fibrosis and active cardiac remodeling, crucial in conditions like heart failure, post-myocardial infarction remodeling, and hypertrophic cardiomyopathy. This review highlights the expanding clinical applications of FAPI-based PET imaging across oncology, inflammation, and cardiovascular disease. While the current data are promising, further large-scale studies and multicenter trials are essential to validate these findings and establish standardized protocols. The versatility and broad applicability of FAPI PET underscore its potential as a transformative tool in precision medicine.

FAP-Targeted SPECT/CT and PET/CT Imaging for Breast Cancer Patients

ABSTRACT

Breast cancer presents a significant global health challenge, necessitating continued innovation in diagnostic and therapeutic approaches. Recent advances have led to the identification of cancer-associated fibroblasts, which are highly prevalent in breast cancers and express fibroblast activation proteins (FAPs), as critical targets. FAP-specific radiotracers, when used with PET/CT and SPECT/CT, have significant potential for improving early breast cancer detection, staging, treatment response monitoring, and therapeutic intervention. This review provides insight into FAP-targeted molecular imaging, exploring advanced techniques for protein status assessment, development of early-phase targeted therapies, and other emerging applications. The advent of FAP-targeted imaging stands to significantly enhance personalized oncologic care, leading to improved breast cancer management and overall patient outcomes.

PET Imaging of Breast Cancer: Current Applications and Future Directions

As molecular imaging use expands for patients with breast cancer, it is important for breast radiologists to have a basic understanding of molecular imaging, including PET. Although breast radiologists may not directly interpret such studies, basic knowledge of molecular imaging will enable the radiologist to better direct diagnostic workup of patients as well as discuss diagnostic imaging with the patient and other treating physicians. Several new tracers are now available to complement imaging glucose metabolism with FDG. Because it provides a noninvasive assessment of disease status across the whole body, PET offers specific advantages over tissue-based assays. Paired with targeted therapy, molecular imaging has the potential to guide personalized treatment of breast cancer, including guiding dosing during drug trials as well as predicting and assessing clinical response. This review discusses the current established applications of FDG, which remains the most widely used PET radiotracer for malignancy, including breast cancer, and highlights potential areas for expanded use based on recent research. It also summarizes research to date on the U.S. Food and Drug Administration (FDA)-approved PET tracer 16α-18F-fluoro-17β-estradiol (FES), which targets ER, including the current guidelines from the Society of Nuclear Medicine and Molecular Imaging on the appropriate use of FES-PET/CT for breast cancer as well as areas of active investigation for other potential applications. Finally, the review highlights several of the most promising novel PET tracers that are poised for clinical translation in the near future.

Clinical Explorations of [68Ga] Ga-FAPI-04 and [18F] FDG Dual-Tracer Total-body PET/CT and PET/MR Imaging

Fibroblast activation protein inhibitor (FAPI) and [18F]fluorodeoxyglucose ([18F]FDG) provide complementary biological information, and FAPI/FDG dual-tracer imaging clinical application is increasing recently. However, optimal protocols for FAPI/FDG dual-tracer positron emission tomography/computed tomography (PET/CT) and PET/magnetic resonance (PET/MR) imaging are still under investigation. Due to its high sensitivity, total-body PET/CT allows for imaging with minimal tracer activity and supports the creation of new dual-tracer PET/CT imaging protocols. PET/MR, with its multiparametric MR imaging, provides additional biological information for diagnosis. Studies have investigated the clinical feasibility of low-activity PET/MR imaging, yielding promising results. As there are still few institutions in the world that have experience with the advances provided by the use of total-body PET/CT and equipped with a PET/MR scanner, we have discussed the clinical explorations to reduce radiation exposure and optimize workflows for [68Ga]Ga-FAPI-04 and [18F]FDG dual-tracer PET/CT and PET/MR imaging. The review also provides potential new clinical explorations of [68Ga]Ga-FAPI-04 and [18F]FDG dual-tracer total-body PET/CT and PET/MR imaging, including dual-tracer dual-low-activity imaging.

Predicting Pathologic Complete Response in Locally Advanced Rectal Cancer with [68Ga]Ga-FAPI-04 PET, [18F]FDG PET, and Contrast-Enhanced MRI: Lesion-to-Lesion Comparison with Pathology

Neoadjuvant therapy in patients with locally advanced rectal cancer (LARC) has achieved good pathologic complete response (pCR) rates, potentially eliminating the need for surgical intervention. This study investigated preoperative methods for predicting pCR after neoadjuvant short-course radiotherapy (SCRT) combined with immunochemotherapy. Methods: Treatment-naïve patients with histologically confirmed LARC were enrolled from February 2023 to July 2023. Before surgery, the patients received neoadjuvant SCRT followed by 2 cycles of capecitabine and oxaliplatin plus camrelizumab. 68Ga-labeled fibroblast activation protein inhibitor ([68Ga]Ga-FAPI-04) PET/MRI, [18F]FDG PET/CT, and contrast-enhanced MRI were performed before treatment initiation and before surgery in each patient. PET and MRI features and the size and number of lesions were also collected from each scan. Each parameter's sensitivity, specificity, and diagnostic cutoff were derived via receiver-operating-characteristic curve analysis. Results: Twenty eligible patients (13 men, 7 women; mean age, 60.2 y) were enrolled and completed the entire trial, and all patients had proficient mismatch repair or microsatellite-stable LARC. A postoperative pCR was achieved in 9 patients (45.0%). In the visual evaluation, both [68Ga]Ga-FAPI-04 PET/MRI and [18F]FDG PET/CT were limited to forecasting pCR. Contrast-enhanced MRI had a low sensitivity of 55.56% to predict pCR. In the quantitative evaluation, [68Ga]Ga-FAPI-04 change in SULpeak percentage, where SULpeak is SUVpeak standardized by lean body mass, had the largest area under the curve (0.929) with high specificity (sensitivity, 77.78%; specificity, 100.0%; cutoff, 63.92%). Conclusion: [68Ga]Ga-FAPI-04 PET/MRI is a promising imaging modality for predicting pCR after SCRT combined with immunochemotherapy. The SULpeak decrease exceeding 63.92% may provide valuable guidance in selecting patients who can forgo surgery after neoadjuvant therapy.

A pilot study of [68Ga]Ga-fibroblast activation protein inhibitor-04 PET/CT in renal cell carcinoma

OBJECTIVES

As a promising positron emission tomography (PET) tracer, [68Ga]Ga-fibroblast activation protein inhibitor-04([68Ga]Ga-FAPI-04) performs better than 2-[18F]fluoro-2-deoxy-d-glucose ([18F]FDG) at diagnosing primary and metastatic lesions in patients with various types of cancer. We investigated the utility of [68Ga]Ga-FAPI-04 PET/CT for the detection of primary and metastatic lesions in renal cell carcinoma (RCC). [18F]FDG PET/CT were used for comparison.

METHODS

Twenty-two patients with suspected RCC or recurrent RCC were enrolled in our study. Among these patients, 14 were newly diagnosed with RCC, 3 had recurrent RCC, and 5 were excluded from further analysis due to having benign renal tumours. Seventeen patients with RCC underwent [68Ga]Ga-FAPI-04 PET/CT, and 6 of them also received [18F]FDG PET/CT. The positive detection rates were calculated and compared with those in patients who underwent both scans.

RESULTS

Data from 17 patients with RCC (median age: 60.5 years, interquartile range [IQR]: 54-70 years) were evaluated. The positive detection rate of [68Ga]Ga-FAPI-04 PET/CT for RCC was 64.7% (11/17). Lymph node metastases (n = 44), lung metastasis (n = 1), and bone metastasis (n = 1) were detected. Six patients with RCC underwent [68Ga]Ga-FAPI-04 and [18F]FDG PET/CT. [68Ga]Ga-FAPI-04 PET/CT showed a higher positive detection rate than [18F]FDG PET/CT in detecting RCC (83.3% [5/6] vs. 50% [3/6], P = 0.545). Additionally, [68Ga]Ga-FAPI-04 PET/CT has higher SUVmax (3.20 [IQR: 2.91-5.80 vs. 2.71 [IQR: 2.13-3.10], P = 0.116) and tumour-to-background ratio (TBR) values (1.60 [IQR: 1.33-3.67] vs. 0.86 [0.48-1.21], P = 0.028) than [18F]FDG PET/CT.

CONCLUSIONS

These findings suggest that [68Ga]Ga-FAPI-04 PET/CT has potential value in RCC diagnosis. Further studies are warranted to validate these results.

ADVANCES IN KNOWLEDGE

Clinical utility of [68Ga]Ga-FAPI-04 in RCC remains unclear, and there are not many similar studies in the literature. We evaluated the role of [68Ga]Ga-FAPI-04 in diagnosing RCC.

PET/MRI and Novel Targets for Breast Cancer

Breast cancer, with its global prevalence and impact on women's health, necessitates effective early detection and accurate staging for optimal patient outcomes. Traditional imaging modalities such as mammography, ultrasound, and dynamic contrast-enhanced magnetic resonance imaging (MRI) play crucial roles in local-regional assessment, while bone scintigraphy and 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) aid in evaluating distant metastasis. Despite the proven utility of 18F-FDG PET/CT in various cancers, its limitations in breast cancer, such as high false-negative rates for small and low-grade tumors, have driven exploration into novel targets for PET radiotracers, including estrogen receptor, human epidermal growth factor receptor-2, fibroblast activation protein, and hypoxia. The advent of PET/MRI, which combines metabolic PET information with high anatomical detail from MRI, has emerged as a promising tool for breast cancer diagnosis, staging, treatment response assessment, and restaging. Technical advancements including the integration of PET and MRI, considerations in patient preparation, and optimized imaging protocols contribute to the success of dedicated breast and whole-body PET/MRI. This comprehensive review offers the current technical aspects and clinical applications of PET/MRI for breast cancer. Additionally, novel targets in breast cancer for PET radiotracers beyond glucose metabolism are explored.