Are we reproducible in measurement of NET liver metastasis?

Proposal of early CT morphological criteria for response of liver metastases to systemic treatments in gastroenteropancreatic neuroendocrine tumors: Alternatives to RECIST

RECIST 1.1 criteria are commonly used with computed tomography (CT) to evaluate the efficacy of systemic treatments in patients with neuroendocrine tumors (NETs) and liver metastases (LMs), but their relevance is questioned in this setting. We aimed to explore alternative criteria using different numbers of measured LMs and thresholds of size and density variation. We retrospectively studied patients with advanced pancreatic or small intestine NETs with LMs, treated with systemic treatment in the first-and/or second-line, without early progression, in 14 European expert centers. We compared time to treatment failure (TTF) between responders and non-responders according to various criteria defined by 0%, 10%, 20% or 30% decrease in the sum of LM size, and/or by 10%, 15% or 20% decrease in LM density, measured on two, three or five LMs, on baseline (≤1 month before treatment initiation) and first revaluation (≤6 months) contrast-enhanced CT scans. Multivariable Cox proportional hazard models were performed to adjust the association between response criteria and TTF on prognostic factors. We included 129 systemic treatments (long-acting somatostatin analogs 41.9%, chemotherapy 26.4%, targeted therapies 31.8%), administered as first-line (53.5%) or second-line therapies (46.5%) in 91 patients. A decrease ≥10% in the size of three LMs was the response criterion that best predicted prolonged TTF, with significance at multivariable analysis (HR 1.90; 95% CI: 1.06-3.40; p = .03). Conversely, response defined by RECIST 1.1 did not predict prolonged TTF (p = .91), and neither did criteria based on changes in LM density. A ≥10% decrease in size of three LMs could be a more clinically relevant criterion than the current 30% threshold utilized by RECIST 1.1 for the evaluation of treatment efficacy in patients with advanced NETs. Its implementation in clinical trials is mandatory for prospective validation. Criteria based on changes in LM density were not predictive of treatment efficacy. CLINICAL TRIAL REGISTRATION: Registered at CNIL-CERB, Assistance publique hopitaux de Paris as "E-NETNET-L-E-CT" July 2018. No number was assigned. Approved by the Medical Ethics Review Board of University Medical Center Groningen.

Are recist criteria adequate in assessing the response to therapy in metastatic NEN?

Response to therapy criteria, known as RECIST (Response Evaluation Criteria in Solid Tumours), are widely used to evaluate neuroendocrine tumours (NET) metastatic to the liver, under treatment. RECIST criteria does not take in account many various distinct features such as tumour growth, secretory capacity and anatomical localisation with wide variation in clinical and biological presentation of different NETs. Key features of RECIST includes definitions of the minimal size of measurable lesions, instructions on how many lesions to measure and follow, and the use of unidimensional, rather than bidimensional, measures for overall evaluation of tumour burden. These measures are currently done with computed tomography (CT) or Magnetic Resonance Imaging (MRI). RECIST criteria are accurate in assessing tumour progression but sometimes inaccurate in assessing tumour response after locoregional therapy or under molecular targeted therapy, tumour vessels being part of the target of such treatments. There is poor correlation between a so called tumour necrosis and conventional methods of response assessment, which poses questions of how best to quantify efficacy of these targeted therapies. Variations in tumour density with computed tomography (CT) could theoretically be associated with tumour necrosis. This hypothesis has been studied proposing alternative CT criteria of response evaluation in metastatic digestive NET treated with targeted therapy. If preliminary results upon the poor relationship between density measured with CT (derived from CHOI criteria) evolution curves at CT and PFS are confirmed by further studies, showing that the correlation between density changing and response to non-targeted treatment is weak, the use of contrast injection, will probably be not mandatory to enable appropriate evaluation.

Optimization of timing of hepatocellular phase imaging after gadoxetate disodium injection for evaluation of patients with neuroendocrine tumor

PURPOSE

Metastatic gastroenteropancreatic neuroendocrine neoplasms (mGEP-NEN) are indolent malignancies which undergo frequent imaging follow-up. Hepatocellular phase (HCP) MR with hepatocellular-specific contrast agent is widely used to evaluate mGEP-NEN liver metastases but is commonly performed after a 20-min delay which prolongs scan time. The purpose of this study was to evaluate if HCP MR at 15 min offers comparable performance to 20-min delay for patients with mGEP-NEN undergoing routine imaging surveillance.

MATERIALS AND METHODS

In this IRB-approved retrospective study, we evaluated 52 patients with mGEP-NEN who were imaged for routine surveillance with gadoxetate disodium (Eovist^®)-enhanced MR including 15- and 20-min delayed HCP. Two readers (R1, R2), blinded to HCP timing, independently reviewed each set of images in random order at least 1 month apart. Readers assessed presence and conspicuity of metastases, and subjective image quality using 5-point scales. Readers quantified the number of metastases and diameter of the largest lesion. Statistical analysis was performed to determine individual-reader and inter-reader differences for qualitative and quantitative data.

RESULTS

No differences were observed for subjective image quality (R1 p = 0.86, R2 p = 0.17) or lesion conspicuity (R1 p = 0.56, R2 p = 0.74) at 15 min and 20 min for either reader. Individual-reader concordance correlation coefficient between 15 and 20 min was high for number of metastases detected (R1 = 0.9842, R2 = 0.9579) and diameter of largest metastasis (R1 = 0.9629, R2 = 0.8859).

CONCLUSION

HCP imaging at 15 min provides similar diagnostic yield to standard 20-min delay, which may help reduce the scan time and costs, and improve throughput and patient satisfaction.

The combination of hepatobiliary phase with Gd-EOB-DTPA and DWI is highly accurate for the detection and characterization of liver metastases from neuroendocrine tumor

OBJECTIVES

To compare the diagnostic accuracy of dynamic contrast-enhanced phases, hepatobiliary phase (HBP), and diffusion-weighted imaging (DWI) for the detection of liver metastases from neuroendocrine tumor (NET).

METHODS

Sixty-seven patients with suspected NET liver metastases underwent gadoxetic acid-enhanced MRI. Three radiologists read four imaging sets separately and independently: DWI, T2W+dynamic, T2WI+HBP, and DWI+HBP. Reference standard included all imaging, histological findings, and clinical data. Sensitivity and specificity were calculated and compared for each imaging set. Interreader agreement was evaluated by intraclass correlation coefficient (ICC). Univariate logistic regression was performed to evaluate lesion characteristics (size, ADC, and enhancing pattern) associated to false positive and negative lesions.

RESULTS

Six hundred twenty-five lesions (545 metastases, 80 benign lesions) were identified. Detection rate was significantly higher combining DWI+HBP than the other imaging sets (sensitivity 86% (95% confidence interval (CI) 0.845-0.878), specificity 94% (95% CI 0.901-0.961)). The sensitivity and specificity of the other sets were 82% and 65% for DWI, 88% and 69% for T2WI, and 90% and 82% for HBP+T2WI, respectively. The interreader agreement was statistically higher for both HBP sets (ICC = 0.96 (95% CI 0.94-0.97) for T2WI+HBP and ICC = 0.91 (95% CI 0.87-0.94) for DWI+HBP, respectively) compared with that for DWI (ICC = 0.76 (95% CI 0.66-0.83)) and T2+dynamic (ICC = 0.85 (95% CI 0.79-0.9)). High ADC values, large lesion size, and hypervascular pattern lowered the risk of false negative.

CONCLUSION

Given the high diagnostic accuracy of combining DWI+HBP, gadoxetic acid-enhanced MRI is to be considered in NET patients with suspected liver metastases. Fast MRI protocol using T2WI, DWI, and HBP is of interest in this population.

KEY POINTS

• The combined set of diffusion-weighted (DW) and hepatobiliary phase (HBP) images yields the highest sensitivity and specificity for neuroendocrine liver metastasis (NELM) detection. • Gadoxetic acid should be the contrast agent of choice for liver MRI in NET patients. • The combined set of HBP and DWI sequences could also be used as a tool of abbreviated MRI in follow-up or assessment of treatment such as somatostatin analogs.

Tumor Contrast-Enhancement for Monitoring of PRRT 177Lu-DOTATATE in Pancreatic Neuroendocrine Tumor Patients

Background: Therapy monitoring of cancer treatment by contrast-enhanced CT (CECT), applying response evaluation criteria in solid tumors criteria version 1. 1 (RECIST 1.1) is less suitable for neuroendocrine tumors (NETs) which, when responding, tend to show stabilization rather than shrinkage. New methods are needed to further classify patients in order to identify non-responders at an early stage and avoid unnecessary adverse effects and costs. Changes in arterial tumor attenuation and contrast-enhancement could be used to identify the effect of therapy, perhaps even in early stages of treatment.

Methods: Patients with metastatic pancreatic NETs (PNETs) receiving peptide receptor radionuclide therapy (PRRT) with ¹⁷⁷Lu-DOTATATE underwent CECT at baseline, mid-treatment (PRRT cycles 3–5) and at follow-up, 3 months after the last PRRT cycle. At baseline CECT, the liver metastasis with the highest arterial attenuation was identified in each patient. The fold changes in arterial tumor attenuation (Hounsfield Units, HU), contrast-enhancement (HU), and transversal tumor area (cm²) between CECT at baseline, mid-treatment and follow-up were calculated. Correlation of the tumor metrics to outcome parameters such as progression-free survival (PFS) and time to best response was performed.

Results: Fifty-two patients were included (27 men, 25 women), median age 60 years (range 29–80), median Ki-67 8% (range 1–30). Six patients had grade 1 PNETs, forty had grade 2 and four had grade 3 tumors. As an internal control, it was first tested and established that the tumor contrast-enhancement was not merely related to that of the abdominal aorta. The mean ± SD arterial attenuation of the liver metastases was similar at baseline, 217 ± 62 HU and at mid-treatment, 238 ± 80 HU and then decreased to 198 ± 62 HU at follow-up, compared to baseline (p = 0.024, n = 52) and mid-treatment (p = 0.0004, n = 43). The transversal tumor area decreased 25% between baseline and follow-up (p = 0.013, n = 52). Tumor contrast-enhancement increased slightly from baseline to mid-treatment and these fold changes correlated with PFS (R² = 0.33, p = 0.0002, n = 37) and with time to best response (R² = 0.34, p < 0.0001, n = 37).

Conclusions: Early changes in contrast-enhancement and arterial attenuation in PNET liver metastases may for CECT monitoring of PRRT yield complementary information to evaluation by RECIST 1.1.