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Background: Real-time intraoperative discrimination of malignant tissue during pediatric solid tumor resection is limited, constraining margin optimization; the utility of indocyanine green (ICG) fluorescence in this population remains incompletely defined. Study Design: Prospective, observational, multi-institutional study (2019–2023) of pediatric, adolescent, and young adult patients undergoing resection of intra-abdominal solid malignancies following preoperative ICG administration. The primary endpoint was diagnostic accuracy of ICG fluorescence for tumor-containing specimens; secondary endpoints included association with margin status and surgeon-perceived intraoperative benefit. Results: Forty-three operations in 42 patients yielded 55 specimens, of which 47 (85%) were malignant. Diagnostic performance was highest in hepatic tumors (sensitivity 83%, positive predictive value 83%) and lower in adrenal and heterogeneous tumor types. ICG avidity was not associated with improved negative margin rates (86% vs 75%, p=0.47). Surgeons reported intraoperative benefit in 67% of cases, most commonly improved visualization. No ICG-related adverse events occurred. Conclusions: ICG fluorescence provides reliable tumor identification in hepatic malignancies but does not correlate with margin-negative resection, indicating limited utility for margin guidance. These data support tumor-specific application and further investigation of optimized fluorescence strategies, including dosing, timing, and alternative fluorophores, in pediatric oncologic surgery.

ABSTRACT Purpose Malignant rhabdoid tumor of the kidney (MRTK) is a rare, aggressive tumor seen in young children. The optimal timing of resection for locally advanced tumors is not well‐defined. The purpose of this study is to evaluate modern oncologic outcomes and the impact of surgical timing. Methods A multicenter retrospective review was performed by institutions participating in the Pediatric Surgical Oncology Research Collaborative. Children younger than 21 years old with MRTK diagnosed between 2000 and 2022 were included. Results Sixty‐nine patients were identified with MRTK and met the inclusion criteria. Median age of diagnosis was 10.1 months. Overall survival (OS) at 1, 5, and 10 years was 49%, 32%, and 19%, respectively. Patients with local Stage III disease who underwent upfront resection ( n = 18) compared to those who had delayed resection after NAT ( n = 15) had a similar OS, median OS greater than 60 months versus 14.6 months, respectively; p = 0.396. The surgical timing groups were balanced in terms of the presence of metastasis, length of follow‐up, and tumor characteristics. There was one occurrence of primary intraoperative tumor spill and two occurrences of organ injury in the upfront resection group compared to none in the delayed resection group. Conclusion MRTK carries a poor prognosis despite multimodal treatment. Histologic diagnosis may not be confirmed at presentation, and MRTK cannot be reliably distinguished from Wilms tumor on imaging alone. As overall survival is similar, the decision regarding surgical timing in locally advanced tumors should be individualized based on perceived resectability, balancing the risk of intraoperative complications against the possibility of tumor progression during neoadjuvant therapy.

ABSTRACT Background Sentinel lymph node (SLN) biopsy is a critical staging tool in skin and soft tissue cancers. Although technetium lymphoscintigraphy is the most common adjunct, indocyanine green (ICG) demonstrates a promising alternative in pediatric, adolescent, and young adult (AYA) skin and soft tissue cancers. Methods and Objectives Evaluate the safety and efficacy of ICG in SLN biopsy (SLNB) in diverse pediatric and AYA solid cancers in a multi‐institutional environment. This is a prospective, observational study conducted at 13 member institutions in the Pediatric Surgical Oncology Research Collaborative between 2019 and 2023. Eligible patients underwent SLNB for primary or recurrent solid skin and soft tissue tumors. Peritumoral ICG was administered intraoperatively. Outcomes included SLN detection rates, histopathology of excised specimens, and surgeon‐reported assessment of utility. Safety was assessed through adverse event reporting. Results Forty SLNB procedures yielded 84 specimens: 13 melanoma (32.5%), 12 squamous cell carcinoma (30%), 11 non‐rhabdomyosarcoma soft tissue sarcoma (27.5%), two rhabdomyosarcoma (5%), one Ewing sarcoma (2.5%), and one malignant peripheral nerve sheath tumor (2.5%). Histologic evaluation identified 81 lymph nodes, 75 benign (89.3%) and six malignant (7.1%); three specimens were adipose tissue (3.6%). Of 81 lymph nodes, 76% were ICG‐positive. ICG had a sensitivity of 79.5%, a specificity of 33%, and a positive predictive value of 96%. All malignant nodes were ICG‐avid. There were no adverse reactions to ICG at 30 days. Conclusions ICG is a safe and effective adjunct for SLNB in pediatric and AYA soft tissue and skin malignancies.

ABSTRACT Introduction Children with hepatoblastoma (HB) and other solid tumors frequently undergo intraoperative blood transfusion (IBT) with unknown impact on oncologic outcomes and scant data to guide transfusion in this population. This study tested the hypothesis that IBT is associated with poorer survival in children with HB. Methods A multicenter retrospective observational study of patients aged <18 years with HB who underwent primary tumor resection, including liver transplantation, from 2010 to 2019 was performed at 19 institutions. The association of IBT with risk of recurrence and death were determined using propensity score reweighted (PSR) Cox proportional hazards regression analyses. Results There were 338 patients identified who met inclusion criteria and had sufficient data for inclusion. Of those, 257 (76%) received IBT, including 253 (98%) who received packed red blood cells (pRBC), 84 (33%) who received plasma, and 28 (11%) who received platelets. IBT was associated with higher pretreatment extent of disease ( p < 0.001), presence of annotation factors (+VPEFR: 50%, n = 129 vs. 37%, n = 30, p = 0.035), and complex resections (extended, meso‐, or total hepatectomy: 54%, n = 139 vs. 27%, n = 22, p < 0.001); these differences were mitigated after applying propensity score weighting. Patients who received IBT had greater postoperative hemoglobin (g/dL) (median 10 (I8–11) vs. 9 (8–10), p = 0.013) and required more postoperative plasma and platelet transfusions ( p < 0.05). Median follow‐up was 4.4 (2.0–8.3) years. Compared with non‐IBT patients, those with IBT had higher incidence of death (PSR HR 2.35, 95% CI 1.10–5.02). Recurrence did not significantly differ across groups (PSR HR = 0.82, 95% CI 0.45–1.48). Conclusion IBT was associated with greater hazard of death. Postoperative hemoglobin levels suggested that unnecessary transfusions occurred and a pRBC‐focused approach to IBT led to coagulopathy. Development of optimal transfusion strategies for HB are needed to minimize unnecessary transfusions.

ABSTRACTBackgroundRenal medullary carcinoma (RMC) is an aggressive tumor associated with sickle cell trait. Despite treatment advances for other rare renal tumors, RMC survival remains poor. We aimed to describe the contemporary management and survival of children and adults with RMC.ProcedureIn this multicenter retrospective cohort study, Pediatric Surgical Oncology Research Collaborative sites searched their databases for patients diagnosed with RMC (2000–2022). Descriptive statistics were calculated and survival analyses performed using Kaplan–Meier and Cox regression.ResultsThirty‐four patients with RMC were identified. Median age was 19 years (IQR: 15–28; range: 7–52). Most were male (24/34; 71%), Black (27/32; 84%), had sickle cell trait or disease (30/33; 91%), presented with metastatic disease (27/34; 79%), and were symptomatic at presentation (32/34; 94%). Median overall survival (OS) was 24 months from diagnosis (16 months for children, 28 months for adults, p = 0.6). Receipt of platinum‐based chemotherapy (23/34; 68%) was associated with significantly higher OS than other regimens (35 vs. 5 months, p < 0.001). Nephrectomy (24/34; 71%) was associated with significantly improved OS compared with non‐operative management (34 vs. 7 months, p = 0.001). Immunotherapy, targeted therapy, or radiation therapy were not associated with significant differences in OS, nor were age, sex, race, sickle cell status, SMARCB1/INI‐1, stage, nephrectomy approach, retroperitoneal lymph node dissection, gross residual disease, margins, or tumor size.ConclusionsRMC survival remains poor despite newer therapies. Nephrectomy and platinum‐based chemotherapy should be considered in locally advanced and metastatic disease. Coordinated international cooperative group studies are needed to meaningfully improve RMC survival.

Abstract Purpose Our objectives were to compare overall survival (OS) and pulmonary relapse between patients with metastatic Ewing sarcoma (EWS) at diagnosis who achieve rapid complete response (RCR) and those with residual pulmonary nodules after induction chemotherapy (non‐RCR). Patients and methods This retrospective cohort study included children under 20 years with metastatic EWS treated from 2007 to 2020 at 19 institutions in the Pediatric Surgical Oncology Research Collaborative. Chi‐square tests were conducted for differences among groups. Kaplan–Meier curves were generated for OS and pulmonary relapse. Results Among 148 patients with metastatic EWS at diagnosis, 61 (41.2%) achieved RCR. Five‐year OS was 71.2% for patients who achieved RCR, and 50.2% for those without RCR ( p = .04), and in multivariable regression among patients with isolated pulmonary metastases, RCR (hazards ratio [HR] 0.42; 95% confidence interval [CI]: 0.17–0.99) and whole lung irradiation (WLI) (HR 0.35; 95% CI: 0.16–0.77) were associated with improved survival. Pulmonary relapse occurred in 57 (37%) patients, including 18 (29%) in the RCR and 36 (41%) in the non‐RCR groups ( p = .14). Five‐year pulmonary relapse rates did not significantly differ based on RCR (33.0%) versus non‐RCR (47.0%, p = .13), or WLI (38.8%) versus no WLI (46.0%, p = .32). Discussion Patients with EWS who had isolated pulmonary metastases at diagnosis had improved OS if they achieved RCR and received WLI, despite having no significant differences in rates of pulmonary relapse.

AbstractBackgroundUndifferentiated embryonal sarcoma of the liver (UESL) is a rare tumor for which there are few evidence‐based guidelines. The aim of this study was to define current management strategies and outcomes for these patients using a multi‐institutional dataset curated by the Pediatric Surgical Oncology Research Collaborative.MethodsData were collected retrospectively for patients with UESL treated across 17 children's hospitals in North America from 1989 to 2019. Factors analyzed included patient and tumor characteristics, PRETEXT group, operative details, and neoadjuvant/adjuvant regimens. Event‐free and overall survival (EFS, OS) were the primary and secondary outcomes, respectively.ResultsSeventy‐eight patients were identified with a median age of 9.9 years [interquartile range [IQR): 7–12]. Twenty‐seven patients underwent resection at diagnosis, and 47 patients underwent delayed resection, including eight liver transplants. Neoadjuvant chemotherapy led to a median change in maximum tumor diameter of 1.6 cm [IQR: 0.0–4.4] and greater than 90% tumor necrosis in 79% of the patients undergoing delayed resection. R0 resections were accomplished in 63 patients (81%). Univariate analysis found that metastatic disease impacted OS, and completeness of resection impacted both EFS and OS, while multivariate analysis revealed that R0 resection was associated with decreased expected hazards of experiencing an event [hazard ratio (HR): 0.14, 95% confidence interval (CI): 0.04–0.6]. At a median follow‐up of 4 years [IQR: 2–8], the EFS was 70.0% [95% CI: 60%–82%] and OS was 83% [95% CI: 75%–93%].ConclusionComplete resection is associated with improved survival for patients with UESL. Neoadjuvant chemotherapy causes minimal radiographic response, but significant tumor necrosis.

Objective: To determine the impact of nodal basin ultrasound (US) surveillance versus completion lymph node dissection (CLND) in children and adolescents with sentinel lymph node (SLN) positive melanoma. Background: Treatment for children and adolescents with melanoma are extrapolated from adult trials. However, there is increasing evidence that important clinical and biological differences exist between pediatric and adult melanoma. Methods: Patients ≤18 years diagnosed with cutaneous melanoma between 2010 and 2020 from 14 pediatric hospitals were included. Data extracted included demographics, histopathology, nodal basin strategies, surveillance intervals, and survival information. Results: Of 252 patients, 90.1% (n=227) underwent SLN biopsy (SLNB), 50.9% (n=115) had at least 1 positive node. A total of 67 patients underwent CLND with 97.0% (n=65/67) performed after a positive SLNB. In contrast, 46 total patients underwent US observation of nodal basins with 78.3% (n=36/46) of these occurring after positive SLNB. Younger patients were more likely to undergo US surveillance (median age 8.5 y) than CLND (median age 11.3 y; P=0.0103). Overall, 8.9% (n=21/235) experienced disease recurrence: 6 primary, 6 nodal, and 9 distant. There was no difference in recurrence (11.1% vs 18.8%; P=0.28) or death from disease (2.2% vs 9.7%; P=0.36) for those who underwent US versus CLND, respectively. Conclusions: Children and adolescents with cutaneous melanoma frequently have nodal metastases identified by SLN. Recurrence was more common among patients with thicker primary lesions and positive SLN. No significant differences in oncologic outcomes were observed with US surveillance and CLND following the identification of a positive SLN.

11535 Background: Twenty-five percent of patients with Ewing Sarcoma (EWS) have metastatic disease at diagnosis, most commonly in the lungs. Our objectives were to compare overall (OS) and pulmonary disease-free survival (PDFS) between patients with metastatic EWS at diagnosis who achieve rapid complete response (RCR), defined as radiographic resolution of all pulmonary nodules at the end of induction chemotherapy, and those with residual pulmonary nodules after induction chemotherapy (non-RCR). Methods: This multi-center, retrospective cohort study included children under 20 years of age with metastatic EWS treated from 2007-2020 at 19 institutions participating in the Pediatric Surgical Oncology Research Collaborative. Chi-square tests were conducted for differences among groups, and p < 0.05 was considered significant. Kaplan-Meier curves were generated for OS and PDFS. Cox regression was performed for OS, controlling for whole lung irradiation (WLI), extrapulmonary metastases, and age. Results: Among 153 patients with metastatic EWS at diagnosis, 61 (40%) achieved RCR, and 87 (57%) did not (5 unknown). The median number of pulmonary nodules was 3.5 in the RCR vs 5 in the non-RCR groups (p = 0.02), while bilateral disease was present in 44 (72%) RCR vs 75 (86%) non-RCR patients (p = 0.03). Pulmonary relapse occurred in 58 (38%) patients, including 18 (29%) in the RCR and 36 (41%) in the non-RCR groups (p = 0.14). Factors associated with pulmonary relapse in the univariate analysis include median age [15 years (IQR: 12-17) with pulmonary relapse vs 12 years (IQR: 9-16) without (p = 0.03)] and extrapulmonary metastases at diagnosis [24 (41%) patients with pulmonary relapse vs 26 (27%) patients without pulmonary relapse (p = 0.05)]. WLI was performed in 100 patients and was not associated with a reduction in pulmonary relapse (p = 0.93). Complete surgical clearance of pulmonary disease was attempted in 29 (19%) patients, including 17 of the patients who met the criteria for RCR. On Kaplan-Meier analyses, 5-year PDFS did not significantly differ based on RCR (67%) vs. non-RCR (53%, p = 0.13), or WLI (61%) vs. no WLI (54%, p = 0.32). However, 5-year OS did vary significantly between patients with RCR and WLI (85%), RCR without WLI (55%), non-RCR with WLI (60%), and non-RCR without WLI (25%; p < 0.01). In Cox regression analysis, RCR was associated with improved OS after controlling for WLI, extrapulmonary metastases, and patient age (HR 0.51, p = 0.03). Conclusions: Patients with EWS who had pulmonary metastases at diagnosis had improved OS if they achieved RCR and received WLI, despite having no significant differences in rates of pulmonary relapse. Further research is needed to determine whether clearance of pulmonary disease achieved through surgical metastasectomy provides a comparable survival benefit and if any subsets of patients have a reduced risk of pulmonary relapse after resection.

AbstractWilms tumor (WT) is the most common renal malignancy in children. Children with favorable histology WT achieve survival rates of over 90%. Twelve percent of patients present with metastatic disease, most commonly to the lungs. The presence of a pleural effusion at the time of diagnosis of WT may be noted on staging imaging; however, minimal data exist regarding the significance and prognostic importance of this finding. The objectives of our study are to identify the incidence of pleural effusions in patients with WT, and to determine the potential impact on oncologic outcomes. A multi‐institutional retrospective review was performed from January 2009 to December 2019, including children with WT and a pleural effusion on diagnostic imaging treated at Pediatric Surgical Oncology Research Collaborative (PSORC) participating institutions. Of 1259 children with a new WT diagnosis, 94 (7.5%) had a pleural effusion. Patients with a pleural effusion were older than those without (median 4.3 vs 3.5 years; P = .004), and advanced stages were more common (local stage III 85.9% vs 51.9%; P < .0001). Only 14 patients underwent a thoracentesis for fluid evaluation; 3 had cytopathologic evidence of malignant cells. Event‐free and overall survival of all children with WT and pleural effusions was 86.2% and 91.5%, respectively. The rate and significance of malignant cells present in pleural fluid is unknown due to low incidence of cytopathologic analysis in our cohort; therefore, the presence of an effusion does not appear to necessitate a change in therapy. Excellent survival can be expected with current stage‐specific treatment regimens.