Quantitative diffusion-weighted MRI response assessment in rhabdomyosarcoma: an international retrospective study on behalf of the European paediatric Soft tissue sarcoma Study Group Imaging Committee.

OBJECTIVE: To investigate the feasibility of diffusion-weighted magnetic resonance imaging (DW-MRI) as a predictive imaging marker after neoadjuvant chemotherapy in patients with rhabdomyosarcoma. MATERIAL AND METHODS: We performed a multicenter retrospective study including pediatric, adolescent and young adult patients with rhabdomyosarcoma, Intergroup Rhabdomyosarcoma Study group III/IV, treated according to the European paediatric Soft tissue sarcoma Study Group (EpSSG) RMS2005 or MTS2008 studies. DW-MRI was performed according to institutional protocols. We performed two-dimensional single-slice tumor delineation. Areas of necrosis or hemorrhage were delineated to be excluded in the primary analysis. Mean, median and 5th and 95th apparent diffusion coefficient (ADC) were extracted. RESULTS: Of 134 included patients, 82 had measurable tumor at diagnosis and response and DW-MRI scans of adequate quality and were included in the analysis. Technical heterogeneity in scan acquisition protocols and scanners was observed. Mean ADC at diagnosis was 1.1 (95% confidence interval [CI]: 1.1-1.2) (all ADC expressed in * 10-3 mm2/s), versus 1.6 (1.5-1.6) at response assessment. The 5th percentile ADC was 0.8 (0.7-0.9) at diagnosis and 1.1 (1.0-1.2) at response. Absolute change in mean ADC after neoadjuvant chemotherapy was 0.4 (0.3-0.5). Exploratory analyses for association between ADC and clinical parameters showed a significant difference in mean ADC at diagnosis for alveolar versus embryonal histology. Landmark analysis at nine weeks after the date of diagnosis showed no significant association (hazard ratio 1.3 [0.6-3.2]) between the mean ADC change and event-free survival. CONCLUSION: A significant change in the 5th percentile and the mean ADC after chemotherapy was observed. Strong heterogeneity was identified in DW-MRI acquisition protocols between centers and in individual patients.

Response Assessment in Paediatric Phase I Trials According to RECIST Guidelines: Survival Outcomes, Patterns of Progression and Relevance of Changes in Tumour Measurements.

INTRODUCTION: RECIST guidelines constitute the reference for radiological response assessment in most paediatric trials of anticancer agents. However, these criteria have not been validated in children. We evaluated the outcomes and patterns of progression of children/adolescents enrolled in phase I trials in two paediatric drug development units. METHODS: Patients aged ≤21 assessed with RECIST (v1.0 or v1.1) were eligible. Clinico-radiological data were analysed using Mann-Whitney U and log-rank tests to correlate response categories and sum of longest diameters (SLD) with time-to-event variables and overall survival (OS). RESULTS: Sixty-one patients (71 enrolments) were evaluated; median age: 12.7 years (range, 3.1-20.9). Overall, 7% achieved complete/partial response (n = 5) and 31% disease stabilisation (n = 22). Median (95% CI) OS (in months) was 29.1 (27.6-30.6) with complete/partial response, 8.9 (2.0-15.8) with stable disease and 2.8 (2.3-3.3) with disease progression (P < 0.001); 32.6% patients with measurable disease presented exclusive progression of existing non-target lesions and/or new lesions. The change in SLD at best response showed a linear correlation with duration of response (r = -0.605; P = 0.004) and time on trial (r = -0.61; P = 0.003), but the change in SLD at progression did not correlate with time to progression (r = -0.219; P = 0.206). CONCLUSIONS: Response assessment according to RECIST correlated with OS in children/adolescents treated on phase I trials. The reduction in SLD at best response correlated with more prolonged responses. Tumour size did not constitute an optimal method to assess disease progression in one third of patients with measurable disease. Further refinement of current response assessment guidelines will enable the development of paediatric-specific radiological criteria.