Wolfgang A. Weber

Use of Positron Emission Tomography for Response Assessment of Lymphoma: Consensus of the Imaging Subcommittee of International Harmonization Project in Lymphoma

PURPOSE To develop guidelines for performing and interpreting positron emission tomography (PET) imaging for treatment assessment in patients with lymphoma both in clinical practice and in clinical trials. METHODS An International Harmonization Project (IHP) was convened to discuss standardization of clinical trial parameters in lymphoma. An imaging subcommittee developed consensus recommendations based on published PET literature and the collective expertise of its members in the use of PET in lymphoma. Only recommendations subsequently endorsed by all IHP subcommittees were adopted. RECOMMENDATIONS PET after completion of therapy should be performed at least 3 weeks, and preferably at 6 to 8 weeks, after chemotherapy or chemoimmunotherapy, and 8 to 12 weeks after radiation or chemoradiotherapy. Visual assessment alone is adequate for interpreting PET findings as positive or negative when assessing response after completion of therapy. Mediastinal blood pool activity is recommended as the reference background activity to define PET positivity for a residual mass > or = 2 cm in greatest transverse diameter, regardless of its location. A smaller residual mass or a normal sized lymph node (ie, < or = 1 x 1 cm in diameter) should be considered positive if its activity is above that of the surrounding background. Specific criteria for defining PET positivity in the liver, spleen, lung, and bone marrow are also proposed. Use of attenuation-corrected PET is strongly encouraged. Use of PET for treatment monitoring during a course of therapy should only be done in a clinical trial or as part of a prospective registry.

FDG PET and PET/CT: EANM procedure guidelines for tumour PET imaging: version 1.0

The aim of this guideline is to provide a minimum standard for the acquisition and interpretation of PET and PET/CT scans with [18F]-fluorodeoxyglucose (FDG). This guideline will therefore address general information about [18F]-fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET/CT) and is provided to help the physician and physicist to assist to carrying out, interpret, and document quantitative FDG PET/CT examinations, but will concentrate on the optimisation of diagnostic quality and quantitative information.

Impact of tumor-specific targeting on the biodistribution and efficacy of siRNA nanoparticles measured by multimodality in vivo imaging.

Targeted delivery represents a promising approach for the development of safer and more effective therapeutics for oncology applications. Although macromolecules accumulate nonspecifically in tumors through the enhanced permeability and retention (EPR) effect, previous studies using nanoparticles to deliver chemotherapeutics or siRNA demonstrated that attachment of cell-specific targeting ligands to the surface of nanoparticles leads to enhanced potency relative to nontargeted formulations. Here, we use positron emission tomography (PET) and bioluminescent imaging to quantify the in vivo biodistribution and function of nanoparticles formed with cyclodextrin-containing polycations and siRNA. Conjugation of 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid to the 5′ end of the siRNA molecules allows labeling with 64Cu for PET imaging. Bioluminescent imaging of mice bearing luciferase-expressing Neuro2A s.c. tumors before and after PET imaging enables correlation of functional efficacy with biodistribution data. Although both nontargeted and transferrin-targeted siRNA nanoparticles exhibit similar biodistribution and tumor localization by PET, transferrin-targeted siRNA nanoparticles reduce tumor luciferase activity by ≈50% relative to nontargeted siRNA nanoparticles 1 d after injection. Compartmental modeling is used to show that the primary advantage of targeted nanoparticles is associated with processes involved in cellular uptake in tumor cells rather than overall tumor localization. Optimization of internalization may therefore be key for the development of effective nanoparticle-based targeted therapeutics.

Positron Emission Tomography in Non–Small-Cell Lung Cancer: Prediction of Response to Chemotherapy by Quantitative Assessment of Glucose Use

PURPOSE To prospectively evaluate the use of positron emission tomography with the glucose analog fluorodeoxyglucose (FDG-PET) to predict response to chemotherapy in patients with advanced non-small-cell lung cancer (NSCLC). PATIENTS AND METHODS Patients with stage IIIB or IV NSCLC scheduled to undergo platinum-based chemotherapy were eligible for this study. Patients were studied by FDG-PET before and after the first cycle of therapy. Based on previous studies, a reduction of tumor FDG uptake by more than 20% as assessed by standardized uptake values (SUV) was used as a criterion for a metabolic response. Furthermore, changes in tumor SUVs were compared with changes in FDG net-influx constants (Ki) and tumor/muscle ratios (t/m). RESULTS Fifty-seven patients were included in the study. There was a close correlation between metabolic response and best response to therapy according to Response Evaluation Criteria in Solid Tumors (P <.0001; sensitivity and specificity for prediction of best response, 95% and 74%, respectively). Median time to progression and overall survival were significantly longer for metabolic responders than for metabolic nonresponders (163 v 54 days and 252 days v 151 days, respectively). Similar results were obtained when Ki was used to assess tumor glucose use, whereas changes in t/m showed considerable overlap between responding and nonresponding tumors. CONCLUSION In NSCLC, reduction of metabolic activity after one cycle of chemotherapy is closely correlated with final outcome of therapy. Using metabolic response as an end point may shorten the duration of phase II studies evaluating new cytotoxic drugs and may decrease the morbidity and costs of therapy in nonresponding patients.

Time Course of Tumor Metabolic Activity During Chemoradiotherapy of Esophageal Squamous Cell Carcinoma and Response to Treatment

PURPOSE To evaluate the time course of therapy-induced changes in tumor glucose use during chemoradiotherapy of esophageal squamous cell carcinoma (ESCC) and to correlate the reduction of metabolic activity with histopathologic tumor response and patient survival. PATIENTS AND METHODS Thirty-eight patients with histologically proven intrathoracic ESCC (cT3, cN0/+, cM0) scheduled to undergo a 4-week course of preoperative simultaneous chemoradiotherapy followed by esophagectomy were included. Patients underwent positron emission tomography with the glucose analog fluorodeoxyglucose (FDG-PET) before therapy (n = 38), after 2 weeks of initiation of therapy (n = 27), and preoperatively (3 to 4 weeks after chemoradiotherapy; n = 38). Tumor metabolic activity was quantitatively assessed by standardized uptake values (SUVs). Results Mean tumor FDG uptake before therapy was 9.3 +/- 2.8 SUV and decreased to 5.7 +/- 1.9 SUV 14 days after initiation of chemoradiotherapy (-38% +/- 18%; P <.0001). The preoperative scan showed an additional decrease of metabolic activity to 3.3 +/- 1.1 SUV (P <.0001). In histopathologic responders (< 10% viable cells in the resected specimen), the decrease in SUV from baseline to day 14 was 44% +/- 15%, whereas it was only 21% +/- 14% in nonresponders (P =.0055). Metabolic changes at this time point were also correlated with patient survival (P =.011). In the preoperative scan, tumor metabolic activity had decreased by 70% +/- 11% in histopathologic responders and 51% +/- 21% in histopathologic nonresponders. CONCLUSION Changes in tumor metabolic activity after 14 days of preoperative chemoradiotherapy are significantly correlated with tumor response and patient survival. This suggests that FDG-PET might be used to identify nonresponders early during neoadjuvant chemoradiotherapy, allowing for early modifications of the treatment protocol.

Metabolic Imaging Predicts Response, Survival, and Recurrence in Adenocarcinomas of the Esophagogastric Junction

PURPOSE A previous study suggested that measurement of therapy-induced changes in tumor glucose metabolism by positron emission tomography (PET) with the glucose analog [18F]fluorodeoxyglucose (FDG) allows to select patients most likely to benefit from preoperative chemotherapy in adenocarcinomas of the esophagogastric junction (AEG). The aim of this study was to prospectively validate these findings by using an a priori definition of metabolic response. PATIENTS AND METHODS Sixty-five patients with locally advanced AEGs were included. Tumor glucose utilization was quantitatively assessed by FDG-PET before chemotherapy and 14 days after initiation of therapy. Patients were classified as metabolic responders when the metabolic activity of the primary tumor had decreased by more than 35% at the time of the second PET. RESULTS Metabolic responders showed a high histopathologic response rate (44%) with a 3-year survival rate of 70%. In contrast, prognosis was poor for metabolic nonresponders with a histopathologic response rate of 5% (P = .001) and a 3-year survival rate of 35% (P = .01). A multivariate analysis (covariates: ypT-, ypN-category, histopathologic response) demonstrated that metabolic response was the only factor predicting recurrence (P = .018) in the subgroup of completely resected (R0) patients. CONCLUSION This study prospectively demonstrates that changes in tumor metabolic activity during chemotherapy predict response, prognosis, and recurrence. These data provide the basis for clinical trials in which preoperative treatment is changed for patients without a metabolic response early in the course of therapy. PET-guided induction therapy may even be applicable to earlier tumor stages because surgery is only minimally delayed in nonresponding patients.

Positron Emission Tomography Using [18F]Galacto-RGD Identifies the Level of Integrin αvβ3 Expression in Man

Purpose: The integrin αvβ3 plays a key role in angiogenesis and tumor cell metastasis and is therefore an important target for new therapeutic and diagnostic strategies. We have developed [18F]Galacto-RGD, a highly αvβ3-selective tracer for positron emission tomography (PET). Here, we show, in man, that the intensity of [18F]Galacto-RGD uptake correlates with αvβ3 expression. Experimental Design: Nineteen patients with solid tumors (musculoskeletal system, n = 10; melanoma, n = 4; head and neck cancer, n = 2; gliobastoma, n = 2; and breast cancer, n = 1) were examined with PET using [18F]Galacto-RGD before surgical removal of the tumor lesions. Snap-frozen specimens (n = 26) were collected from representative areas with low and intense standardized uptake values (SUV) of [18F]Galacto-RGD. Immunohistochemistry was done using the αvβ3-specific antibody LM609. Intensity of staining (graded on a four-point scale) and the microvessel density of αvβ3-positive vessels were determined and correlated with SUV and tumor/blood ratios (T/B). Results: Two tumors showed no tracer uptake (mean SUV, 0.5 ± 0.1). All other tumors showed tracer accumulation with SUVs ranging from 1.2 to 10.0 (mean, 3.8 ± 2.3; T/B, 3.4 ± 2.2; tumor/muscle ratio, 7.7 ± 5.4). The correlation of SUV and T/B with the intensity of immunohistochemical staining (Spearmans r = 0.92; P < 0.0001) as well as with the microvessel density (Spearmans r = 0.84; P < 0.0001) were significant. Immunohistochemistry confirmed lack of αvβ3 expression in normal tissue (benign lymph nodes, muscle) and in the two tumors without tracer uptake. Conclusions: Molecular imaging of αvβ3 expression with [18F]Galacto-RGD in humans correlates with αvβ3 expression as determined by immunohistochemistry. PET with [18F]Galacto-RGD might therefore be used as a new marker of angiogenesis and for individualized planning of therapeutic strategies with αvβ3-targeted drugs.

Positron Emission Tomography As an Imaging Biomarker

Positron emission tomography (PET) allows noninvasive, quantitative studies of various biologic processes in the tumor tissue. By using PET, investigators can study the pharmacokinetics of anticancer drugs, identify various therapeutic targets and monitor the inhibition of these targets during therapy. Furthermore, PET provides various markers to assess tumor response early in the course of therapy. A significant number of studies have now shown that changes in tumor glucose utilization during the first weeks of chemotherapy are significantly correlated with patient outcome. These data suggest that PET may be used as a sensitive test to assess the activity of new cytotoxic agents in phase II studies. Furthermore, early identification of nonresponding tumors provides the opportunity to adjust treatment regimens according to the individual chemosensitivity of the tumor tissue. However, further prospective and randomized validation of PET is still required before PET controlled chemotherapy can be used in clinical practice.

Tumor Cell Metabolism Imaging

Molecular imaging of tumor metabolism has gained considerable interest, since preclinical studies have indicated a close relationship between the activation of various oncogenes and alterations of cellular metabolism. Furthermore, several clinical trials have shown that metabolic imaging can significantly impact patient management by improving tumor staging, restaging, radiation treatment planning, and monitoring of tumor response to therapy. In this review, we summarize recent data on the molecular mechanisms underlying the increased metabolic activity of cancer cells and discuss imaging techniques for studies of tumor glucose, lipid, and amino acid metabolism.

TNFR1 Signaling and IFN-γ Signaling Determine whether T Cells Induce Tumor Dormancy or Promote Multistage Carcinogenesis

Immune responses may arrest tumor growth by inducing tumor dormancy. The mechanisms leading to either tumor dormancy or promotion of multistage carcinogenesis by adaptive immunity are poorly characterized. Analyzing T antigen (Tag)-induced multistage carcinogenesis in pancreatic islets, we show that Tag-specific CD4+ T cells home selectively into the tumor microenvironment around the islets, where they either arrest or promote transition of dysplastic islets into islet carcinomas. Through combined TNFR1 signaling and IFN-gamma signaling, Tag-specific CD4+ T cells induce antiangiogenic chemokines and prevent alpha(v)beta(3) integrin expression, tumor angiogenesis, tumor cell proliferation, and multistage carcinogenesis, without destroying Tag-expressing islet cells. In the absence of either TNFR1 signaling or IFN-gamma signaling, the same T cells paradoxically promote angiogenesis and multistage carcinogenesis. Thus, tumor-specific T cells can directly survey multistage carcinogenesis through cytokine signaling.