Prognostic Value of Pretreatment Metabolic Tumor Volume and Total Lesion Glycolysis Using 18F-FDG PET/CT in Patients With Metastatic Renal Cell Carcinoma Treated With Anti-Vascular Endothelial Growth Factor-Targeted Agents

m6A-regulated tumor glycolysis: new advances in epigenetics and metabolism

Glycolytic reprogramming is one of the most important features of cancer and plays an integral role in the progression of cancer. In cancer cells, changes in glucose metabolism meet the needs of self-proliferation, angiogenesis and lymphangiogenesis, metastasis, and also affect the immune escape, prognosis evaluation and therapeutic effect of cancer. The n6-methyladenosine (m6A) modification of RNA is widespread in eukaryotic cells. Dynamic and reversible m6A modifications are widely involved in the regulation of cancer stem cell renewal and differentiation, tumor therapy resistance, tumor microenvironment, tumor immune escape, and tumor metabolism. Lately, more and more evidences show that m6A modification can affect the glycolysis process of tumors in a variety of ways to regulate the biological behavior of tumors. In this review, we discussed the role of glycolysis in tumor genesis and development, and elaborated in detail the profound impact of m6A modification on different tumor by regulating glycolysis. We believe that m6A modified glycolysis has great significance and potential for tumor treatment.

Molecular and functional imaging in cancer-targeted therapy: current applications and future directions

Targeted anticancer drugs block cancer cell growth by interfering with specific signaling pathways vital to carcinogenesis and tumor growth rather than harming all rapidly dividing cells as in cytotoxic chemotherapy. The Response Evaluation Criteria in Solid Tumor (RECIST) system has been used to assess tumor response to therapy via changes in the size of target lesions as measured by calipers, conventional anatomically based imaging modalities such as computed tomography (CT), and magnetic resonance imaging (MRI), and other imaging methods. However, RECIST is sometimes inaccurate in assessing the efficacy of targeted therapy drugs because of the poor correlation between tumor size and treatment-induced tumor necrosis or shrinkage. This approach might also result in delayed identification of response when the therapy does confer a reduction in tumor size. Innovative molecular imaging techniques have rapidly gained importance in the dawning era of targeted therapy as they can visualize, characterize, and quantify biological processes at the cellular, subcellular, or even molecular level rather than at the anatomical level. This review summarizes different targeted cell signaling pathways, various molecular imaging techniques, and developed probes. Moreover, the application of molecular imaging for evaluating treatment response and related clinical outcome is also systematically outlined. In the future, more attention should be paid to promoting the clinical translation of molecular imaging in evaluating the sensitivity to targeted therapy with biocompatible probes. In particular, multimodal imaging technologies incorporating advanced artificial intelligence should be developed to comprehensively and accurately assess cancer-targeted therapy, in addition to RECIST-based methods.

Genomic Profiling and Response to Immune Checkpoint Inhibition plus Tyrosine Kinase Inhibition in FH-Deficient Renal Cell Carcinoma

BACKGROUND

FH-deficient renal cell carcinoma (RCC) is a rare and exceptionally aggressive RCC subtype. There is currently limited understanding of the molecular alterations, pathogenesis, survival outcomes, and systemic therapy efficacy for this cancer.

OBJECTIVE

To perform a retrospective multicenter analysis of molecular profiling and clinical outcomes for patients with FH-deficient RCC, with an emphasis on treatment response to first-line immune checkpoint inhibitor plus tyrosine kinase inhibitor (ICI/TKI) versus bevacizumab plus erlotinib (Bev/Erlo) combination therapy in patients with advanced disease.

DESIGN, SETTING, AND PARTICIPANTS

The study included 77 cases of FH-deficient RCC from 15 centers across China.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Clinical characteristics, molecular correlates, ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography imaging, and treatment outcomes were analyzed.

RESULTS AND LIMITATIONS

A total of 77 patients were identified, including 70 cases with a germline FH alteration (hereditary leiomyomatosis RCC syndrome [HLRCC]-associated RCC) and seven patients with somatic FH loss. Recurrent pathogenic alterations were found in NF2 (six/57, 11%), CDH1 (six/57, 11%), PIK3CA (six/57, 11%), and TP53 (five/57, 8.8%). Sixty-seven patients were evaluable for response to first-line systemic therapy with Bev/Erlo (n = 12), TKI monotherapy (n = 29), or ICI/TKI (n = 26). ICI/TKI combination therapy was associated with more favorable overall survival on systemic treatment (hazard ratio [HR] 0.19, 95% confidence interval [CI] 0.04-0.90) and progression-free survival on first-line therapy (HR 0.22, 95% CI 0.07-0.71) compared to Bev/Erlo combination therapy. The main limitation is the retrospective study design.

CONCLUSIONS

We described the genomic characteristics of FH-deficient RCC in an Asian population and observed a favorable response to ICI/TKI combinational therapy among patients with advanced disease.

PATIENT SUMMARY

This real-world study provides evidence supporting the antitumour activity of combining molecular targeted therapy plus immunotherapy for kidney cancer deficient in fumarate hydratase. Further studies are needed to investigate the efficacy of this combination strategy in this rare cancer.

Targeted Molecular Imaging as a Biomarker in Urologic Oncology

Urologic malignancies constitute a large portion of annually diagnosed cancers. Timely diagnosis, accurate staging, and assessment of tumor heterogeneity are essential to devising the best treatment strategy for individual patients. The high sensitivity of molecular imaging allows for early and sensitive detection of lesions that were not readily detectable using conventional imaging techniques. Moreover, molecular imaging enables the interrogation of molecular processes used in targeted cancer therapies and predicts cancer response to treatment. Here we review the current advancements in molecular imaging of urologic cancers, including prostatic, vesical, renal testicular, and ureteral cancers.

Prognostic significance of 18F-FDG PET/CT indices in metastatic renal cell cancer and evaluation of revised IMDC risk model by including 18F-FDG PET-CT parameters

Background

Prognostic markers in metastatic renal cell cancer (mRCC) are still insufficient. Any prognostic model objectively determines disease burden.

Purpose

To investigate the relationship between 18-fluorodeoxyglucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) parameters and outcomes in mRCC, and to define a revised International Metastatic Renal Cell Carcinoma Database Consortium (IMDC) model for the intermediate-risk group.

Material and Methods

A retrospective study of mRCC was conducted. To investigate the prognostic significance of 18F-FDG PET/CT parameters, maximum standardized uptake value (SUVmax), total lesion glycolysis (TLG), and metabolic tumor volume (MTV) were determined in pre-treatment images. Cutoff values were defined by ROC curve analyses and their association with outcomes was analyzed. Additionally, a TLG-adjusted IMDC model was created by stratifying intermediate-risk group patients according to TLG levels.

Results

The study included 52 patients. The disease control rate (DCR) was 61.5% and median overall survival (OS) was 18 months (95% confidence interval=9.2–25.8). In the univariate analyses, IMDC score, MTV, and TLG were prognostic factors for Disease Control Rate (DCR), and Eastern Cooperative Oncology Group (ECOG)-Performance Status (PS), IMDC score, lactate dehydrogenase (LDH), treatment option, MTV, and TLG were prognostic factors for OS ( P < 0.05 each). In the multivariate analyses, MTV was an independent prognostic factor for DCR, and ECOG-PS, LDH, IMDC score, and TLG were independent prognostic factors for OS. According to the revised-IMDC model, the intermediate-favorable group showed longer OS than the intermediate-unfavorable group.

Conclusion

Pretreatment MTV was independent prognostic factor for DCR and ECOG-PS, LDH, IMDC score, and TLG were independent prognostic factors for OS. Revised-IMDC model could identify patients with a worse prognosis among the IMDC intermediate-risk group.

The value of preoperative 18F-FDG PET metabolic and volumetric parameters in predicting microvascular invasion and postoperative recurrence of hepatocellular carcinoma

BACKGROUND

Microvascular invasion (MVI) is very important in the evaluation of hepatocellular carcinoma (HCC), but diagnosis is determined by postoperative pathology; thus, preoperative noninvasive methods will play an active role. The purpose of the study was to assess the performance of metabolic parameters of preoperative 18F-fluorodeoxyglucose PET/computerized tomography (18F-FDG PET/CT) in the prediction of MVI and postoperative recurrence in primary hepatocellular carcinoma.

METHODS

We retrospectively collected 72 patients with HCC who have performed 18F-FDG PET/CT scan before partial hepatectomy between 2016 and 2019. We used both normal liver tissue and inferior vena cava as the reference background and combined with clinicopathological features, 18F-FDG PET/CT metabolic and volumetric indices to predict MVI and postoperative recurrence of primary HCC before surgery.

RESULTS

Twenty-one of the 72 patients recurred, in recurrent cases showed higher maximum standard uptake value (SUVmax), TNR (ratio of tumor SUVmax to mean SUV [SUVmean] of the background tissue), metabolic tumor volume (MTV) and total lesion glycolysis (TLG) than nonrecurrence cases (P < 0.001). All 18F-FDG PET metabolic and volumetric indices for predicting postoperative HCC recurrence were significant on receiver-operating-characteristic (ROC) curve analyses (P < 0.05). TNRIVC, TNRNL, MTVIVC, MTVNL TLGIVC and TLGNL were significant factors for predicting MVI in HCC (P < 0.05). On multivariate analyses, MVI, SUVmax, TNRIVC, TNRNL, MTVIVC, MTVNL, TLGIVC and TLGNL (P < 0.05) are independent risk factors for predicting postoperative HCC recurrence. TNRIVC is the most relevant PET/CT parameter for predicting MVI in HCC, and MTVIVC is the most valuable for predicting postoperative HCC recurrence. Moreover, the PET/CT parameters are more accurate for prognosis with inferior vena cava as a reference background than with normal liver tissue.

CONCLUSION

18F-FDG PET/CT metabolic and volumetric indices are effective predictors, and could noninvasively provide more comprehensive predictive information on MVI and postoperative recurrence of primary HCC before surgery.

Metabolic Switch in Hepatocellular Carcinoma Patients Treated with Sorafenib: a Proof-of-Concept Trial

BACKGROUND

Sorafenib is a multikinase inhibitor used to treat advanced hepatocellular carcinoma (HCC). Recently, a preclinical trial has shown that response to sorafenib is associated with a metabolic shift towards aerobic glycolysis. To test this observation in humans, we decided to conduct a proof-of-concept trial investigating the role of metabolic shift detected on [¹⁸F]FDG PET/CT in predicting survival and tumor response in HCC patients treated with sorafenib.

METHODS

We prospectively enrolled advanced HCC patients candidate to sorafenib and undergoing [¹⁸F]FDG PET/CT at baseline, at 24 h, and at day 7 following treatment start. Response evaluation was obtained after 8 weeks according to Response Evaluation Criteria in Solid Tumors (RECIST). All clinical variables and metabolic parameters (i.e., SUVmax; metabolic tumor volume, MTV; total lesion glycolysis, TLG; and their variations, Δ) were compared with those of treatment response and correlated to progression-free (PFS) and overall survival (OS).

RESULTS

For this proof-of-concept trial, between August 2016 and August 2018, 13 patients (10 male, 3 female, median age 69) were enrolled. Considering the entire cohort, we demonstrated a significant negative correlation between ΔSUVmax at 24 h and 1 week (rho = - 0.733, p = 0.016). The metabolic shift, as expected, demonstrated median SUVmax, MTV, and TLG after 1 week lower in patients with a stable disease than a progressive disease (p = 0.019). Metabolic parameters and ECOG performance status (PS) resulted significantly correlated to PFS and OS at univariate analysis. On multivariate analysis, only median MTV at 1 week resulted as an independent prognostic factor for PFS (p = 0.033).

CONCLUSIONS

As hypothesized, [¹⁸F]FDG PET/CT resulted in able to evaluate metabolic shift at 24 h and early treatment response already 1 week after treatment start. Moreover, metabolic parameters and ECOG PS resulted in predictive and prognostic factors to PFS and OS, with MTV at 1 week appearing as an independent predictive factor for PFS.

Molecular Imaging of Angiogenesis in Oncology: Current Preclinical and Clinical Status

Angiogenesis is an active process, regulating new vessel growth, and is crucial for the survival and growth of tumours next to other complex factors in the tumour microenvironment. We present possible molecular imaging approaches for tumour vascularisation and vitality, focusing on radiopharmaceuticals (tracers). Molecular imaging in general has become an integrated part of cancer therapy, by bringing relevant insights on tumour angiogenic status. After a structured PubMed search, the resulting publication list was screened for oncology related publications in animals and humans, disregarding any cardiovascular findings. The tracers identified can be subdivided into direct targeting of angiogenesis (i.e., vascular endothelial growth factor, laminin, and fibronectin) and indirect targeting (i.e., glucose metabolism, hypoxia, and matrix metallo-proteases, PSMA). Presenting pre-clinical and clinical data of most tracers proposed in the literature, the indirect targeting agents are not 1:1 correlated with angiogenesis factors but do have a strong prognostic power in a clinical setting, while direct targeting agents show most potential and specificity for assessing tumour vascularisation and vitality. Within the direct agents, the combination of multiple targeting tracers into one agent (multimers) seems most promising. This review demonstrates the present clinical applicability of indirect agents, but also the need for more extensive research in the field of direct targeting of angiogenesis in oncology. Although there is currently no direct tracer that can be singled out, the RGD tracer family seems to show the highest potential therefore we expect one of them to enter the clinical routine.

Role of positron emission tomography/computed tomography in the evaluation of renal cell carcinoma

Introduction:

Positron emission tomography (PET) is not a standard recommendation in most of the major guidelines for the evaluation of renal cell carcinoma (RCC). Earlier studies evaluating PET scan in patients with RCC have provided discordant results. However, with the advent of newer hybrid PET/computed tomography (CT) scanning systems, this modality has shown increased efficacy in the evaluation of primary renal masses along with the detection of extrarenal metastases, restaging recurrent RCC, and also in monitoring response to targeted therapy. We performed a systematic review of the existing literature on the role of PET scan in the evaluation of RCC.

Methodology:

We systematically searched the databases of PubMed/Medline, Embase, and Google Scholar to identify studies on the use of PET scan in RCC. Using Preferred Reporting Items for Systematic Reviews and Meta-analysis guidelines, 94 full-text articles were selected, of which 54 relevant articles were then reviewed, after a consensus by the authors.

Results:

Several studies have shown similar sensitivity and specificity of fluoro-2-deoxy-2-d-glucose-PET (FDG-PET) scan as compared to conventional CT scan for the initial diagnosis of RCC, and an improved sensitivity and specificity for the detection of metastases and recurrences following curative therapy. The PET scan may also play a role in predicting the initial tumor biology and pathology and predicting the prognosis as well as the response to therapy.

Conclusion:

The current guidelines do not recommend PET scan in the staging armamentarium of RCCs. However, FDG-PET scan is as efficacious, if not better than conventional imaging alone, in the evaluation of the primary and metastatic RCC, as well as in evaluating the response to therapy, due to its ability to pick up areas of increased metabolic activity early on. Newer tracers such as ^Ga68 prostate specific membrane antigen-labeled ligands may help in opening up newer avenues of theragnostics.

Elevated tumor-to-liver standardized uptake value ratio (TLR) from preoperative 18F-FDG PET/CT predicts poor prognosis of patients with clear cell renal cell carcinoma after nephrectomy

AIM

To assess the potential of using preoperative ¹⁸F-FDG PET/CT to predict the prognosis of patients with clear cell renal cell carcinoma (ccRCC) after nephrectomy.

METHODS

Sixty-nine patients with newly diagnosed ccRCC who underwent ¹⁸F-FDG PET/CT prior to surgery were retrospectively reviewed. The metabolic parameters of maximum standardized uptake value (SUVmax) and tumor-to-liver ratio (TLR) from ¹⁸F-FDG PET/CT were obtained. Clinicopathological characteristics, including the World Health Organization/the International Society of Urological Pathology (WHO/ISUP) grade, pathological tumor node metastasis (pTNM) stage, venous tumor thrombus, and so on, were acquired. Univariate and multivariate Cox proportional hazards analyses were performed to identify the prognostic factors for disease-free survival (DFS).

RESULTS

Of the 69 patients, 25 patients (36.2%) experienced disease progression during the follow-up period. In univariate analysis, the primary tumor size (>4.85 cm), pTNM stage (Ⅲ/Ⅳ), WHO/ISUP grade (G3/4), venous tumor thrombus, adjuvant therapy, SUVmax (>3.55), and TLR (>1.66) were found to correlate with the incidence of decreased DFS (P < 0.05). In multivariate analysis, TLR (P = 0.007, HR: 5.489, 95%CI: 1.605-18.774) and pTNM stage (P = 0.024, HR: 10.385, 95%CI: 1.361-79.238) were revealed to serve as independent prognostic predictors for DFS after adjustment for other variables. Only 3 cases (8.3%) with normal TLR showed disease progression, while 22 cases (66.7%) with elevated TLR experienced disease progression.

CONCLUSION

ccRCC patients with preoperatively elevated TLR (>1.66) and high pTNM stages (Ⅲ/Ⅳ) had significantly unfavorable survival outcomes. These patients should be carefully monitored to detect the possibility of disease progression after nephrectomy as early as possible.

Prognostic value of maximum standard uptake value, metabolic tumor volume, and total lesion glycolysis of 18F-FDG PET/CT in patients with renal carcinoma: A protocol for systematic review and meta analysis

PURPOSE

We present a comprehensive systematic review of the documented literature on parameters derived from F-fluorodeoxyglucose positron emission tomography (F-FDG PET) and meta-analysis of the prognostic value of maximal standard uptake value (SUVmax), metabolic tumor volume (MTV) and total lesional glycolysis (TLG) in patients with renal carcinoma (RCC).

PATIENTS AND METHODS

Relevant articles in English from PubMed, EMBASE, and the Cochrane Library were retrieved. Pooled hazard ratio (HR) values were used to assess the prognostic value of SUVmax, MTV, and TLG.

RESULTS

A total of 10 primary studies involving 780 patients with RCC were included. The combined HRs for event-free survival were 1.32 (95% CI 1.10-1.58) for SUVmax, 2.40 (95% CI 1.20-4.79) for MTV, and 3.31 (95% CI 1.68-6.50) for TLG. Pooled HRs for overall survival were 1.264 (95% CI 1.124-1.421) for SUVmax, 3.52 (95% CI 1.451-8.536) for MTV, and 6.33 (95% CI 1.32-30.30) for TLG. Subgroup analysis revealed SUVmax as an independent risk factor for patients with recurrence or metastasis.

CONCLUSION

The present meta-analysis confirmed that despite the clinical heterogeneity of RCC and adoption of various methods between studies, high SUVmax is a significant prognostic factor, especially in patients with recurrence or metastasis. MTV and TLG were associated with prediction of higher risk of adverse events or death in patients with RCC.

Computational and Experimental Studies of Inhibitor Design for Aldolase A

Glycolytic enzyme fructose-bisphosphate aldolase A is an emerging therapeutic target in cancer. Recently, we have solved the crystal structure of murine aldolase in complex with naphthalene-2,6-diyl bisphosphate (ND1) that served as a template of the design of bisphosphate-based inhibitors. In this work, a series of ND1 analogues containing difluoromethylene (-CF₂), methylene (-CH₂), or aldehyde substitutions were designed. All designed compounds were studied using molecular dynamics (MD) simulations with the AMOEBA force field. Both energetics and structural analyses have been done to understand the calculated binding free energies. The average distances between ligand and protein atoms for ND1 were very similar to those for the ND1 crystal structure, which indicates that our MD simulation is sampling the correct conformation well. CF₂ insertion lowers the binding free energy by 10-15 kcal/mol, while CF₂ substitution slightly increases the binding free energy, which matches the experimental measurement. In addition, we found that NDB with two CF₂ insertions, the strongest binder, is entropically driven, while others including NDA with one CF₂ insertion are all enthalpically driven. This work provides insights into the mechanisms underlying protein-phosphate binding and enhances the capability of applying computational and theoretical frameworks to model, predict, and design diagnostic strategies targeting cancer.

Prognostic value of performance status in metastatic renal cell carcinoma patients receiving tyrosine kinase inhibitors: a systematic review and meta-analysis

BACKGROUND

The association between performance status (PS) and the prognosis of metastatic renal cell carcinoma (mRCC) patients receiving tyrosine kinase inhibitors (TKIs) remains controversial. The aim of this study is to evaluate the prognostic value of PS in mRCC patients treated with TKIs.

METHODS

Electronic databases were searched to identify the studies that had assessed the association between pretreatment PS and prognosis in mRCC patients receiving TKIs. Hazard ratios (HRs) and 95% confidence interval (CI) for overall survival (OS) and progression-free survival (PFS) from eligible studies were used to calculate combined HRs. The heterogeneity across the included studies was assessed by Cochrane's Q test and I² statistic. The Begg's funnel plot and Egger's linear regression teats were used to evaluate the potential publication bias. The meta-analysis was performed with RevMan 5.3 and Stata SE12.0 according to the PRISMA guidelines.

RESULTS

A total of 6780 patients from 19 studies were included in this meta-analysis. The results showed that a poor PS was an effective prognostic factor of both OS (pooled HR: 2.08, 95% CI: 1.78-2.45) and PFS (pooled HR: 1.51, 95% CI: 1.20-1.91). Subgroup analysis revealed that poor PS significantly associated with poor OS and PFS in studies using Karnofsky PS scale (OS, pooled HR: 2.20, 95% CI: 1.65-2.94; PFS, pooled HR: 1.74, 95% CI: 1.19-2.56), conducted in Asia (OS, pooled HR: 2.25, 95% CI: 1.71-2.95; PFS, pooled HR: 1.73, 95% CI: 1.14-2.64) and Newcastle-Ottawa Scale score of 8 (OS, pooled HR: 2.61, 95% CI: 1.92-3.55; PFS, pooled HR: 2.43, 95% CI: 1.36-4.33).

CONCLUSIONS

This study suggests that a poor PS is significantly associated with poor prognosis in mRCC patients receiving TKIs.

Functional Parameters of 18F-FDG PET/CT in Patients with Primary Testicular Diffuse Large B-Cell Lymphoma

Fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) positron-emission tomography/computed tomography (PET/CT), a hybrid imaging technique that simultaneously provides functional and anatomical information, has been reported to be useful in lymphoma. The present study was to evaluate the functional parameters of ¹⁸F-FDG PET/CT in patients with testicular diffuse large B-cell lymphoma (DLBCL). We retrospectively reviewed medical records of 5095 patients with lymphoma who treated at West China Hospital between March 2003 and January 2017, and selected patients with ¹⁸F-FDG PET/CT findings and subsequently biopsy confirmed the invasion of testis with DLBCL. Maximum standardized uptake values (SUV_max), peak standardized uptake values (SUV_peak), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) of the patients were measured. We evaluated the characteristics of ¹⁸F-FDG PET/CT in this population. Six patients ranged in age from 37 to 73 years (median age, 58 years) were included in the analysis. The mean SUV_max was 11.09 and varied between 7.20 and 19.75; mean SUV_peak was 9.56 and ranged between 6.79 and 14.39. In addition, mean MTV 42% was 18.4 and varied between 1.3 and 61.6; mean MTV 2.5 was 34.7 and varied significantly between 1.6 and 141.9. With regard to TLG, mean TLG 42% was 168.906 and ranged from 7.514 to 687.004, while mean TLG 2.5 was 253.972 and ranged from 8.400 to 1127.802. In conclusion, ¹⁸F-FDG PET/CT scan is a useful tool in patients with testicular DLBCL. SUV, MTV, and TLG may vary a lot in different patients. SUV_max of testicular DLBCL lesion is relatively higher than that of normal testis. Also, we provided a set of MTV and TLG data and firstly showed their significant correlation with overall survival, which indicated a potential prognostic value of MTV and TLG. However, studies with larger population are needed to confirm these findings.

Tyrosine-Kinase Inhibitors Therapies with Mainly Anti-Angiogenic Activity in Advanced Renal Cell Carcinoma: Value of PET/CT in Response Evaluation

Renal cell carcinoma (RCC) is the most frequent renal tumor and the majority of patients are diagnosed with advanced disease. Tumor angiogenesis plays a crucial role in the development and progression of RCC together with hypoxia and glucose metabolism. These three pathways are strictly connected to the cell growth and proliferation, like a loop that is self-feeding. Over the last few years, the ever-deeper knowledge of its contribution in metastatic RCC led to the discovery of numerous tyrosine kinase inhibitors (TKIs) targeting pro-angiogenic receptors at different levels such as sunitinib, sorafenib, pazopanib, axitinib, tivozanib, and dovitinib. As anti-angiogenic agents, TKIs interfere the loop, being able to inhibit tumor proliferation. TKIs are now available treatments for advanced RCC, which demonstrated to improve overall survival and/or progression free survival. Their effects can be detectable early on Positron Emission Tomography/Computed Tomography (PET/CT) by change in ¹⁸F-fluoro-2-deoxy-2-d-glucose (¹⁸F-FDG) uptake, the main radiotracer used to date, as a strong indicator of biological response. ¹⁸F-FDG PET/CT demonstrated an ability to predict and monitor disease progression, allowing an early and reliable identification of responders, and could be used for image-guided optimization and "personalization" of anti-angiogenic regimens. New radiotracers for biometabolic imaging are currently under investigation, which exploit the other pathways involved in the cancer process, including cellular proliferation, aerobic metabolism, cell membrane synthesis, hypoxia and amino acid transport, as well as the angiogenic process, but they require further studies.

Multimodality Imaging in Tumor Angiogenesis: Present Status and Perspectives

Angiogenesis is a complex biological process that plays a central role in progression of tumor growth and metastasis. It led to a search for antiangiogenic molecules, and to design antiangiogenic strategies for cancer treatment. Noninvasive molecular imaging, such as positron emission tomography (PET) and single photon emission computed tomography (SPECT), could be useful for lesion detection, to select patients likely to respond to antiangiogenic therapies, to confirm successful targeting, and dose optimization. Additionally, nuclear imaging techniques could also aid in the development of new angiogenesis-targeted drugs and their validation. Angiogenesis imaging can be categorized as targeted at three major cell types: (I) non-endothelial cell targets, (II) endothelial cell targets, and (III) extracellular matrix proteins and matrix proteases. Even if radiopharmaceuticals studying the metabolism and hypoxia can be also used for the study of angiogenesis, many of the agents used in nuclear imaging for this purpose are yet to be investigated. The purpose of this review is to describe the role of molecular imaging in tumor angiogenesis, highlighting the advances in this field.