Response evaluation: beyond RECIST

Clinical and Translational Research Challenges in Neuroendocrine Tumours

Neuroendocrine tumours (NETs) represent a range of neoplasms that may arise from any (neuro)endocrine cell situated in any part of the human body. As any other rare diseases, NETs face several difficulties in relation to research. This review will describe some of the main challenges and proposed solutions faced by researchers with expertise in rare malignancies. Some of the most common challenges in clinical and translational research are enumerated in this review, covering aspects from clinical, translational and basic research. NETs being a heterogeneous group of diseases and a limited sample size of clinical and translational research projects are the main challenges. Challenges with NETs lay over the disparities between healthcare models to tackle rare diseases. NETs add an extra layer of complexity due to a numerous group of different entities. Prospective real-world data trials are an opportunity for rare cancers with the revolution of electronic health technologies. This review explores potential solutions to these challenges that could be useful not only to the NET community but also to other rare tumours researchers.

Pretreatment Innate Cell Populations and CD4 T Cells in Blood Are Associated With Response to Immune Checkpoint Blockade in Melanoma Patients

The development of changes in T cells, referred to as T cell exhaustion, has been suggested as a cause of primary or acquired resistance to immunotherapy by immune checkpoint blockade (ICB). A limited number of studies, largely performed on tumor infiltrating lymphocytes (TILs), has provided evidence in support of this hypothesis, but whether similar changes occur in circulating blood lymphocytes has received little attention. In the present study, a comprehensive analysis of peripheral blood leukocytes from 42 patients taken over the course of treatment with anti-PD-1 was undertaken. The patients included those grouped as responders (who did not progress), primary non-responders (primary resistance) and those with acquired resistance (who initially responded then subsequently progressed). Analysis included surface markers of exhaustion, production of cytokines following in vitro stimulation, and assessment of transcription factor levels associated with T cell exhaustion. There were differences in innate cell populations between responders and non-responders at baseline and maintained throughout therapy. Frequencies of total and classical CD14⁺CD16^- monocytes were higher and the major subset of NK cells (CD16^hiCD56⁺) was significantly smaller in the primary resistance group compared with responders. However, differences in peripheral blood expression of exhaustion markers were not evident between the treatment groups. T cell exhaustion markers were expressed in practically all patients and the major observation was an increase in CD39 on CD4 T cells during treatment. The results confirm the association of Eomes transcription factor with T cell exhaustion but levels of expression and the ratio with T-bet over Eomes did not differ between the patient groups. Thus, peripheral blood expression of T cell exhaustion markers does not distinguish between responders and non-responders to anti-PD-1 therapy. CD4 T cell expression of IFNγ also differed in pre-treatment samples, indicating that predictors of response unrelated to exhaustion may be present in peripheral blood. The association of response with innate cell populations and CD4 T cell responses requires further study.

Acute Temporal Changes of MRI-Tracked Tumor Vascular Parameters after Combined Anti-angiogenic and Radiation Treatments in a Rat Glioma Model: Identifying Signatures of Synergism

In this study we used magnetic resonance imaging (MRI) biomarkers to monitor the acute temporal changes in tumor vascular physiology with the aim of identifying the vascular signatures that predict response to combined anti-angiogenic and radiation treatments. Forty-three athymic rats implanted with orthotopic U-251 glioma cells were studied for approximately 21 days after implantation. Two MRI studies were performed on each animal, pre- and post-treatment, to measure tumor vascular parameters. Two animal groups received treatment comprised of Cilengitide, an anti-angiogenic agent and radiation. The first group received a subcurative regimen of Cilengitide 1 h before irradiation, while the second group received a curative regimen of Cilengitide 8 h before irradiation. Cilengitide was given as a single dose (4 mg/kg; intraperitoneal) after the pretreatment MRI study and before receiving a 20 Gy radiation dose. After irradiation, the post-treatment MRI study was performed at selected time points: 2, 4, 8 and 12 h (n = ≥5 per time point). Significant changes in vascular parameters were observed at early time points after combined treatments in both treatment groups (1 and 8 h). The temporal changes in vascular parameters in the first group (treated 1 h before exposure) resembled a previously reported pattern associated with radiation exposure alone. Conversely, in the second group (treated 8 h before exposure), all vascular parameters showed an initial response at 2-4 h postirradiation, followed by an apparent lack of response at later time points. The signature time point to define the "synergy" of Cilengitide and radiation was 4 h postirradiation. For example, 4 h after combined treatments using a 1 h separation (which followed the subcurative regimen), tumor blood flow was significantly decreased, nearly 50% below baseline (P = 0.007), whereas 4 h after combined treatments using an 8 h separation (which followed the curative regimen), tumor blood flow was only 10% less than baseline. Comparison between the first and second groups further revealed that most other vascular parameters were maximally different 4 h after combined treatments. In conclusion, the data are consistent with the assertion that the delivery of radiation at the vascular normalization time window of Cilengitide improves radiation treatment outcome. The different vascular responses after the different delivery times of combined treatments in light of the known tumor responses under similar conditions would indicate that timing has a crucial influence on treatment outcome and long-term survival. Tracking acute changes in tumor physiology after monotherapy or combined treatments appears to aid in identifying the beneficial timing for administration, and perhaps has predictive value. Therefore, judicial timing of treatments may result in optimal treatment response.

MiR-99b-5p expression and response to tyrosine kinase inhibitor treatment in clear cell renal cell carcinoma patients

A number of treatments targeting VEGF or mTOR pathways have been approved for metastatic clear cell Renal Cell Carcinoma (ccRCC), but the majority of patients show disease progression after first line therapy with a very low rate of complete or long-term responders. It has been shown that miRs may play a role in prediction of treatment response in various cancer types. The aim of our study was to identify a miR signature predictive for RCC patients' response to antiangiogenic tyrosine kinase inhibitor (TKI) treatment in the first line therapy. Sequencing of 40 paired normal/tumor formalin fixed and paraffin embedded ccRCC tissues revealed separate clustering via unsupervised dendrograms. With supervised analysis, the strongest differential expression was obtained with miR-99b-5p, which was significantly lower in patients with short progression free survival (<8 months) and TKI non-responders (progressive disease patients according to RECIST) (p<0.0001, each). Validation using RTqPCR and a second patient cohort compiled from three different hospitals (n=65) showed higher expression of miR-99b-5p in complete responders, but this trend did not reach statistical significance. It is concluded that low miR-99b-5p expression analyzed with sequencing methodology may correlate with tumor progression in TKI-treated ccRCC patients.

Imaging for Oncologic Response Assessment in Lymphoma

OBJECTIVE

The purpose of this article is to examine the role of different imaging biomarkers, focusing in particular on the use of updated CT and PET response criteria for the assessment of oncologic treatment effectiveness in patients with lymphoma but also discussing other potential functional imaging methods and their limitations.

CONCLUSION

Lymph nodes are commonly involved by metastatic solid tumors as well as by lymphoma. Evolving changes in cancer therapy for lymphoma and metastases have led to improved clinical outcomes. Imaging is a recognized surrogate endpoint that uses established criteria based on changes in tumor bulk to monitor the effects of treatment. With the introduction of targeted therapies and novel antiangiogenic drugs, the oncologic expectations from imaging assessment are changing to move beyond simple morphologic methods. Molecular and functional imaging methods (e.g., PET, perfusion, DWI, and dual-energy CT) are therefore being investigated as imaging biomarkers of response and prognosis. The role of these advanced imaging biomarkers extends beyond measuring tumor burden and therefore might offer insight into early predictors of therapeutic response. Despite the potential benefits of these exciting imaging biomarkers, several challenges currently exist.

Response Assessment Criteria and Their Applications in Lymphoma: Part 1

The effectiveness of cancer therapy, both in individual patients and across populations, requires a systematic and reproducible method for evaluating response to treatment. Early efforts to meet this need resulted in the creation of numerous guidelines for quantifying posttherapy changes in disease extent, both anatomically and metabolically. Over the past few years, criteria for disease response classification have been developed for specific cancer histologies. To date, the spectrum of disease broadly referred to as lymphoma is perhaps the most common for which disease response classification is used. This review article provides an overview of the existing response assessment criteria for lymphoma and highlights their respective methodologies and validities. Concerns over the technical complexity and arbitrary thresholds of many of these criteria, which have impeded the long-standing endeavor of standardizing response assessment, are also discussed.

EASL- and mRECIST-evaluated responses to combination therapy of sorafenib with transarterial chemoembolization predict survival in patients with hepatocellular carcinoma

PURPOSE

Published studies have not investigated the suitability of Response Evaluation Criteria in Solid Tumors (RECIST), European Association for the Study of the Liver (EASL) criteria, and modified RECIST (mRECIST) for assessing the response of patients with hepatocellular carcinoma to treatment with sorafenib combined with transarterial chemoembolization. Here, we aimed to define the earliest time at which the response to combination therapy could be accurately assessed and validate the prognostic value of these criteria at this early posttherapy time point.

EXPERIMENTAL DESIGN

A total of 114 consecutive patients with hepatocellular carcinoma receiving combination therapy were retrospectively enrolled. The therapy response at different time points was assessed using RECIST, EASL, and mRECIST. Cox regression analysis and Kaplan-Meier curves were used to assess overall survival (OS) in the responders and nonresponders.

RESULTS

At the third follow-up (median, 94 days; range, 89-102 days) after therapy, the response rates obtained using EASL (50.6%) and mRECIST (51.6%) were greater than that obtained using RECIST (16.5%). The agreement was strong between the mRECIST and EASL results (k = 0.9) but weak between mRECIST and RECIST (k = 0.3). The EASL and mRECIST responses significantly correlated with survival. Risk reductions of 52% and 50% were observed for EASL and mRECIST responders, respectively, compared with nonresponders. However, no significant association between the treatment response and survival was observed using RECIST.

CONCLUSIONS

The earliest time to evaluate the response to combination therapy is 3 months (median, 94 days) after therapy. EASL and mRECIST responses are independent predictors for OS at this early time point.

Surrogate end points for survival in the target treatment of advanced non-small-cell lung cancer with gefitinib or erlotinib

BACKGROUND

It is controversial for the use of survival surrogate end points including response rate (RR), disease control rate (DCR), time to progression, and progression-free survival (PFS) in trials of molecular targeted agents. Our aim was to determine the correlations of these surrogates with survival in the treatment of advanced non-small-cell lung cancer (ANSCLC) with epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs), gefitinib and erlotinib.

METHODS

Summary data of median survival time (MST) and surrogates from prospective trials of EGFR-TKIs in ANSCLC were identified. Patient- or trial-related characteristics were introduced as covariates. Simple and multivariate linear regression models were fitted for MST and each surrogate, respectively. And the significance of each surrogate as a survival marker was compared by calculating the area under their receiver operating characteristic (ROC) curves.

RESULTS

Sixty eligible trials (9,903 patients) were enrolled. RR, DCR, and PFS were all strongly associated with MST. In their simple linear regression models, the coefficient of determination (R(2)) was 0.83 (p < 0.000001), 0.58 (p < 0.0001), and 0.70 (p < 0.0001), respectively. And in their multivariate linear regression models, the standard coefficient was 0.71 (p < 0.001), 0.40 (p < 0.001), and 0.74 (p < 0.001), respectively, while RR and PFS were the preferred survival predictors in the ROC analysis.

CONCLUSION

RR or PFS may serve as an appropriate survival surrogate in the clinical trials of EGFR-TKIs for ANSCLC.

Observer variability in a phase II trial - assessing consistency in RECIST application

OBJECTIVE

To assess the consistency of Response Evaluation Criteria in Solid Tumours (RECIST) application in a phase II trial.

MATERIAL AND METHODS

Patients with metastatic non-resectable colorectal cancer treated with a combination of an antibody and a chemotherapeutic drug, were included. Computed tomography (CT) scans (thorax, abdomen and pelvis) were performed at baseline and after every fourth treatment cycle. RECIST was intended for response evaluation. The scans were consecutively read by a heterogeneous group of radiologists as a part of daily work and hereafter retrospectively reviewed by a dedicated experienced radiologist. Agreement on best overall response (BOR) between readers and reviewer was quantified using κ-coefficients and the discrepancy rate was correlated with the number of different readers per patient using a χ(2)-test.

RESULTS

One hundred patients with 396 CT scans were included. Discrepancies between the readers and the reviewer were found in 47 patients. The majority of discrepancies concerned the application of RECIST. With the review, BOR changed in 17 patients, although, only in six patients the change was potentially treatment altering. Overall, the κ-coefficient of agreement between readers and reviewer was 0.71 (good). However, in the subgroup of responding patients the κ-coefficient was 0.21 (fair). The number of patients with discrepancies was significantly higher with three or more different readers per patient than with less (p =0.0003).

CONCLUSION

RECIST was not consistently applied and the majority of the reader discrepancies were RECIST related. Post review, 17 patients changed BOR; six patients in a potentially treatment altering manner. Additionally, we found that the part of patients with discrepancies increased significantly with more than three different readers per patient. The findings support a peer-review approach where a few dedicated radiologists perform double blinded readings of all the on-going cancer trial patients' CT scans.

Evaluation of molecular targeted cancer drug by changes in tumor marker doubling times

BACKGROUND

We evaluated the usefulness of tumor marker doubling time (DT) as an efficacy indicator of a molecular targeted anticancer agent.

METHODS

Twenty-five patients with advanced hepatocellular carcinoma (HCC) received TSU-68, a multiple tyrosine kinase inhibitor. Exponential increase in HCC-specific tumor marker levels (alpha-fetoprotein or des-gamma-carboxyprothrombin) was seen in 15 of them prior to TSU-68 administration. The relationship between tumor marker DT and tumor volume DT was evaluated. Next, tumor marker DT in the first 8 weeks of TSU-68 administration was compared with tumor marker DT before treatment. Efficacy evaluation based on changes in tumor marker DT was compared with Response Evaluation Criteria In Solid Tumors (RECIST).

RESULTS

Tumor marker DT and tumor volume DT were almost identical (r(2) = 0.94, P < 0.001) in each patient before TSU-68 administration. Efficacy evaluation based on changes in tumor marker DT on TSU-68 administration was in accordance with RECIST in 12/15 cases. Discordance was observed in three cases, for which RECIST indicated disease progression in spite of elongated tumor marker DT. Those cases showed substantial tumor necrosis without volume shrinkage or appearance of new lesions in spite of apparent effects on target lesions.

CONCLUSIONS

Serum tumor marker DT can be used to evaluate viable tumor burden irrespective of the presence of tumor necrosis which can compromise radiographic evaluation. This approach may be applicable to the evaluation of responses to chemotherapy, particularly to cytostatic agents (ClinicalTrials.gov number, NCT00784290).

Objective assessment of tumour response to therapy based on tumour growth kinetics

Background:

Current standards for assessment of tumour response to therapy (a) categorise therapeutic efficacy values, inappropriate for patient-specific and deterministic studies, (b) neglect the natural growth characteristics of tumours, (c) are based on tumour shrinkage, inappropriate for cytostatic therapies, and (d) do not accommodate integration of functional/biological means of therapeutic efficacy assessed with, for example, positron emission tomography or magnetic resonance imaging, with data from anatomical changes in tumour.

Methods:

A quantity for tumour response was formulated assuming that an effective treatment may decrease the cell proliferation rate (cytostatic) and/or increase the cell loss rate (cytotoxic) of the tumour. Tumour response values were analysed for 11 non-Hodgkin's lymphoma patients treated with ¹³¹I-labelled anti-B1 antibody and 12 prostate cancer patients treated with a nutritional supplement.

Results:

Tumour response was found to be equal to the logarithm of the ratio of post-treatment tumour volume to the volume of corresponding untreated tumour. Neglecting the natural growth characteristics of tumours results in underestimation of treatment effectiveness based on currently used methods. The model also facilitates the integration of data from tumour volume changes, with data from functional imaging.

Conclusion:

Tumour response to therapy can be assessed with a continuous dimensionless quantity for both cytotoxic and cytostatic treatments.

Comparison of different tumor response criteria in patients with hepatocellular carcinoma after systemic therapy with the multikinase inhibitor sorafenib

RATIONALE AND OBJECTIVES

The aim of this study was to compare tumor changes in patients with hepatocellular carcinoma receiving sorafenib using evaluation criteria of the American Association for the Study of Liver Diseases (AASLD) and the European Association for the Study of the Liver (EASL) as opposed to the Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1.

MATERIALS AND METHODS

Twenty-five patients with inoperable hepatocellular carcinoma receiving oral sorafenib underwent magnetic resonance imaging at baseline and follow-up every 8 weeks (range, 2-19 weeks; mean, 7.6 weeks). Data were evaluated retrospectively. Survey time until progression ranged from 5 to 102 weeks (mean, 25.6 weeks), with a total of 54 target lesions being monitored. Additionally, evaluation of serum α-fetoprotein was performed at follow-up.

RESULTS

The best response at follow-up using RECIST resulted in rates of 4% objective response (complete remission or partial remission), 24% (progressive disease), and 72% (stable disease). In contrast, AASLD and EASL criteria identified objective responses in 28% and 48%. Twenty percent of all patients classified as having progressive disease by RECIST were identified as having "pseudo"-progression due to extensive necrosis. Eleven percent of patients classified as having stable disease by RECIST were disclosed as essentially progressive. AASLD area and AASLD diameter disclosed 36% and 40% of patients as having partial remission, respectively, whereas EASL criteria discovered only 24%. There was no significant correlation between serum α-fetoprotein progression and AASLD, EASL, or RECIST evaluation criteria.

CONCLUSIONS

Response monitoring via functional criteria such as AASLD or EASL criteria is likely to more accurately reflect vital tumor burden in hepatocellular carcinoma compared to RECIST.

Tyrosine kinase inhibitors in treating soft tissue sarcomas: sunitinib in non-GIST sarcomas

Sarcomas are uncommon malignancies that represent more than 50 different tumor types. Surgery remains the mainstay of treating localised disease. Anthracycline and ifosfamide-based chemotherapy is an option for advanced disease; however, effective treatment of advanced soft tissue sarcoma remains a challenge. Advances in understanding the genetic nature of cancer have led to the development of new treatment options for sarcoma. Sunitinib malate is an oral multitargeted tyrosine kinase inhibitor with antiangiogenic properties and promising activity in the treatment of GIST refractory to imatinib, however in either soft tissue sarcoma, experience with sunitinib is under development in different clinical trials. In this review we offer the experience with this small molecular target in non-GIST sarcomas.

Response rates: a valuable signal of promising activity?

A main criterion to identify activity in phase II studies is the response rates achieved in a well-defined subset of patients. The response could be defined as a measure of tumor shrinkage. For 30 years, metric methods have been used to assess this response. The World Health Organization was the first organization to propose a unified definition for response status. Over time, the latter evolved and 10 years ago an international consensus panel proposed the Response Evaluation Criteria in Solid Tumors criteria. Although these guidelines for response assessment have limitations and biases, they have nevertheless been proven useful and advantageous. This article reviews those criteria and describes their use.

Early MRI response monitoring of patients with advanced hepatocellular carcinoma under treatment with the multikinase inhibitor sorafenib

Background

New therapeutic principles in clinical oncology require the adjustment of response criteria to govern therapy decisions. For advanced hepatocellular carcinoma (HCC) a new era has recently begun by the approval of the multikinase inhibitor sorafenib. As a unique feature, HCC usually develops in a diseased liver and current imaging technologies employing classical response criteria have not been prospectively evaluated for this new treatment.

Methods

MRI signal patterns were assessed in 21 advanced HCC patients receiving sorafenib. MRI was performed at baseline and in short-term intervals thereafter. Signal changes under therapy on T1WI, T2WI and post-gadolinium images including necrosis volume and its ratio to the entire tumor volume were compared to baseline imaging. To assess the association between the categorical variables, Fisher's exact tests were applied for a statistical analysis. Survey time ranged from 2–65 weeks, and a total of 39 target lesions were evaluated.

Results

Signal abnormalities during sorafenib therapy were disclosed by T1WI and T2WI in 15/21 patients. The predominant tumor signal change was hyperintensity on both T1WI and T2WI. Interestingly, most patients developed MRI signal changes within 4 weeks of therapy; in contrast, two non-responders did not show any signal alteration at follow-up. Under therapy, 16/21 patients presented with new or progressive necrosis, whereas 7 patients achieved temporarily >75% tumor necrosis under sorafenib. Significantly associated MRI variables were increase in T1WI signal and tumor necrosis (p = 0.017) as well as increase of tumor necrosis with an elevated ratio of necrotic to vital tumor areas (p = 0.002). Remarkably, some (3/13) of the patients developing necrotic tumor areas showed a relevant (>20%) increase in tumor volume, which should be considered in the assessment of imaging studies.

Conclusion

As sorafenib induces early intralesional necrosis with profound changes in T1WI/T2WI MRI signal intensities and measurable necrotic tumor areas in most HCC patients, early MRI-based evaluation could pave the way for its rationale and cost-effective application.

Evaluation of the optimal number of lesions needed for tumor evaluation using the response evaluation criteria in solid tumors: a north central cancer treatment group investigation

PURPOSE In February 2000, the criteria for measuring tumor shrinkage as an indicator of antitumor activity were redefined by the Response Evaluation Criteria in Solid Tumors (RECIST). This resulted in simplifying bidimensional to unidimensional measurement of lesions. Under RECIST, all lesions, up to 10, must be measured. Scanning and measuring multiple lesions is costly, time-consuming, and a disincentive to participation in clinical trials. We investigated whether fewer than 10 lesions can be measured without compromising the accuracy of assessing a regimen's activity. PATIENTS AND METHODS Thirty-two North Central Cancer Treatment Group trials including 2,374 patients were analyzed. Twelve studies were conducted before RECIST; 20 were conducted post-RECIST. Agreement between objective status by cycle, confirmed response, overall response rate, and time to progression (TTP) was evaluated based on all 10 versus the largest one through five lesions. Results The median number of lesions reported on RECIST trials did not differ from pre-RECIST trials (median = 2.0). One lesion at baseline was reported in 49% of patients, two lesions in 28% of patients, three lesions in 12% of patients, four lesions in 6% of patients, and five lesions in 5% of patients in post-RECIST trials. Utilizing the largest two lesions produced excellent concordance with that using all lesions for all end points. In no trial did the overall response rate differ by more than 3% when two versus all lesions were considered. Evaluating more than two lesions did not significantly improve agreement. CONCLUSION Based on these trials, the assessment of more than two lesions did not alter the conclusions regarding a treatment's efficacy as judged by response rate or TTP.

The minimum number of target lesions that need to be measured to be representative of the total number of target lesions (according to RECIST)

Response evaluation criteria in solid tumours (RECIST) were introduced as a means to classify tumour response with no definition of the minimum number of lesions. This study was conducted in order to evaluate discrepancies between full assessments based on either all target lesions or fewer lesions. RECIST evaluation was performed on separate occasions based on between one and seven of the target lesions, with simultaneous assessment of non-target lesions. 99 patients were included. 38 patients demonstrated progressive disease, in 61% of whom it was a result of the appearance of new lesions or unequivocal progress in non-target lesions. 32 patients showed stable disease, with 8 having results that differed when 1-3 target lesions were measured. 22 cases were considered as having partial regression, with only 1 case differing when performing 1-3 target lesion assessments. Seven cases demonstrated complete response. The number of discordant cases increased gradually from measuring three lesions to one target lesion. The average number of available target lesions among those with discrepancies was 7.1, which was significantly higher than those demonstrating concordance (4.1 lesions; p<0.05). In conclusion, measuring fewer than four target lesions might cause discrepancies when more than five target lesions are present.

Launching a novel preclinical infrastructure: comparative oncology trials consortium directed therapeutic targeting of TNFalpha to cancer vasculature

Background

Under the direction and sponsorship of the National Cancer Institute, we report on the first pre-clinical trial of the Comparative Oncology Trials Consortium (COTC). The COTC is a novel infrastructure to integrate cancers that naturally develop in pet dogs into the development path of new human drugs. Trials are designed to address questions challenging in conventional preclinical models and early phase human trials. Large animal spontaneous cancer models can be a valuable addition to successful studies of cancer biology and novel therapeutic drug, imaging and device development.

Methodology/Principal Findings

Through this established infrastructure, the first trial of the COTC (COTC001) evaluated a targeted AAV-phage vector delivering tumor necrosis factor (RGD-A-TNF) to αV integrins on tumor endothelium. Trial progress and data was reviewed contemporaneously using a web-enabled electronic reporting system developed for the consortium. Dose-escalation in cohorts of 3 dogs (n = 24) determined an optimal safe dose (5×10¹² transducing units intravenous) of RGD-A-TNF. This demonstrated selective targeting of tumor-associated vasculature and sparing of normal tissues assessed via serial biopsy of both tumor and normal tissue. Repetitive dosing in a cohort of 14 dogs, at the defined optimal dose, was well tolerated and led to objective tumor regression in two dogs (14%), stable disease in six (43%), and disease progression in six (43%) via Response Evaluation Criteria in Solid Tumors (RECIST).

Conclusions/Significance

The first study of the COTC has demonstrated the utility and efficiency of the established infrastructure to inform the development of new cancer drugs within large animal naturally occurring cancer models. The preclinical evaluation of RGD-A-TNF within this network provided valuable and necessary data to complete the design of first-in-man studies.