Houdt, Winan J. van

9524 Background: Unresectable melanoma in-transit metastases (ITM) can pose a significant clinical challenge. Our recently published data comparing first-line treatments for ITM, isolated limb infusion or perfusion (ILI/ILP), immune checkpoint inhibitors (ICI) and intralesional talimogene laherparepvec (TVEC), found superior outcomes with TVEC. However, TVEC was used more often in patients with lower disease burden and earlier stage (IIIB vs. IIIC/D). Therefore, we sought to better investigate these differences with a propensity score-matched (PSM) analysis. Methods: A multi-institutional, international IRB- approved retrospective analysis was conducted for unresectable melanoma ITM from 2016-2022. PSM analysis comparing first-line ILI/ILP, ICI, and TVEC for was performed. Patients were matched for stage, number of ITM, anatomical site, CLND status, gender and age. Kaplan-Meier curves (OS, PFS, DMFS) and Cumulative incidence function (MSS) were used to visualize time-to-event outcomes in the PSM cohort, though both methods do not account for the matched structure. Results: 274 patients were identified, 120 female/154 male; 96 treated with ILI/ILP, 111 with ICI, and 67 with TVEC. Median follow-up was 40 months (range, 1-80). PSM was performed and identified 36 TVEC–ICI pairs and 27 TVEC–ILI pairs. These were combined resulting in a final cohort of 108 observations (45 TVEC, 36 ICI and 27 ILI). The groups were well balanced. No statistical difference was found for metastasis-free survival (DMFS), progression-free survival (PFS), melanoma-specific survival (MSS), and overall survival (OS) between treatment modalities. TVEC was associated with significant improvement in local PFS (median was 2.2 years (y) for ILI/ILP, 1.5y for ICI and not reached for TVEC, p=0.048). While not statistically significant, a clinical benefit was seen in PFS being longer for TVEC (2.1y for TVEC vs. 1.2y for ILI/ILP and 1.1y for ICI; p=0.2) and OS (not reached vs 2.9y for ILI/ILP and 5.2y for ICI; p=0.2). On mixed effect Cox regression proportional hazard model using the matched data set, there were no significant differences in any of the survival and recurrence outcomes. Conclusions: When patients are propensity-matched, there were no significant differences in first-line treatment modalities for unresectable melanoma ITM. Treatment with TVEC did result in clinically meaningful improved overall and local PFS and OS. This supports that selection of ITM therapy should incorporate an individualized approach, incorporating disease distribution, stage, burden, treatment side effects and patient priorities.

Abstract Background Malignant peripheral nerve sheath tumors (MPNSTs) are rare, aggressive sarcomas, with 40% associated with neurofibromatosis type 1 (NF1). Surgical excision is the main treatment for localized disease; however, local recurrence (LR) remains high. Radiotherapy (RTx) is increasingly used to enhance local control in STS, but its use remains controversial due to the potential for increased major wound complications and an increased risk of secondary malignancies in NF1 patients. This study investigated the use and impact of RTx on local control in MPNSTs, particularly in the NF1 setting. Methods Surgically treated primary MPNSTs from 1988 to 2019 in the MONACO multicenter cohort were included. Differences in demographics, treatment, and RTx use between NF1 and non-NF1 cases were examined. Factors influencing RTx administration and LR were assessed via multivariable analyses. Results Among 499 patients (33.1% NF1), 143 (28.7%) experienced LRs. Radiotherapy was administered to 56.3% of patients (57.0% in the NF1 group), with 27.3% receiving neoadjuvant and 72.7% adjuvant RTx. RTx was administered significantly more often to high-grade and extremity tumors. While RTx did not affect overall survival, it reduced LR risk in sporadic cases (hazard ratio [HR] 0.530; 95% confidence interval [CI], 0.354–0.793) but not in the NF1 subgroup (HR 1.00; 95% CI, 0.545–1.85). In NF1 patients, a microscopically positive margin (R1) was the only risk factor for LR development (HR 2.1; 95% CI, 1.19–3.79). Conclusions RTx is frequently used in the treatment of MPNSTs, regardless of NF1 status. While it may affect the LR rate in sporadic cases, its impact on NF1 patients is less clear.

AbstractBackgroundIsolated limb infusion and perfusion (ILI/ILP) has been a mainstay treatment for unresectable melanoma in‐transit metastases (ITM), but increased use of immune checkpoint inhibitors (ICI) and intralesional therapy (talimogene laherparepvec [TVEC]) introduced several different management options. This study compares first‐line ILI/ILP, ICI, and TVEC.MethodsRetrospective review from 12 international institutions included patients treated from 1990 to 2022 with first‐line ILI/ILP, ICI, or TVEC for unresectable melanoma ITM.ResultsA total of 551 patients were treated, with ILI/ILP (n = 356), ICI (n = 125), and TVEC (n = 70) with median follow‐up of 5.5 years. Tumor burden was highest with ILI/ILP and lowest with TVEC (p = .002). Breslow thickness was lowest with TVEC (p = .007). TVEC was mostly used in stage IIIB disease versus IIIC for ILI/ILP and ICI (p = .01). Using ICI as the reference category, TVEC had the highest odds of a complete response (CR) (odds ratio, 1.96; p = .029) and a longer local progression‐free survival (PFS) (hazard ratio [HR], 0.40; p = .003). ILI/ILP had shorter local PFS (HR, 1.72; p = .012), PFS (HR, 1.79; p < .001), distant metastasis‐free survival (DMFS) (HR, 1.75; p = .014), overall survival (HR, 1.82; p = .009), and melanoma‐specific survival (HR, 2.29; p = .004). Stage IIIB disease had longer DMFS (HR, 0.24; p < .001) compared to IIIC/D.ConclusionsTVEC as first‐line therapy for unresectable melanoma ITM was associated with superior CR rates and local PFS. Notably, TVEC was used in patients with a lower Breslow thickness, disease stage, and tumor burden. Therefore, when compared to ILI/ILP and ICI, TVEC should be considered as first‐line therapy for unresectable stage IIIB melanoma ITM with minimal tumor burden and lower Breslow thickness.

Abstract Background This study aimed to assess the performance of currently available risk calculators in a cohort of patients with malignant peripheral nerve sheath tumors (MPNST) and to create an MPNST-specific prognostic model including type-specific predictors for overall survival (OS). Methods This is a retrospective multicenter cohort study of patients with MPNST from 11 secondary or tertiary centers in The Netherlands, Italy and the United States of America. All patients diagnosed with primary MPNST who underwent macroscopically complete surgical resection from 2000 to 2019 were included in this study. A multivariable Cox proportional hazard model for OS was estimated with prespecified predictors (age, grade, size, NF-1 status, triton status, depth, tumor location, and surgical margin). Model performance was assessed for the Sarculator and PERSARC calculators by examining discrimination (C-index) and calibration (calibration plots and observed-expected statistic; O/E-statistic). Internal–external cross-validation by different regions was performed to evaluate the generalizability of the model. Results A total of 507 patients with primary MPNSTs were included from 11 centers in 7 regions. During follow-up (median 8.7 years), 211 patients died. The C-index was 0.60 (95% CI 0.53–0.67) for both Sarculator and PERSARC. The MPNST-specific model had a pooled C-index of 0.69 (95%CI 0.65–0.73) at validation, with adequate discrimination and calibration across regions. Conclusions The MPNST-specific MONACO model can be used to predict 3-, 5-, and 10-year OS in patients with primary MPNST who underwent macroscopically complete surgical resection. Further validation may refine the model to inform patients and physicians on prognosis and support them in shared decision-making.

9574 Background: Surgery remains the gold standard for resectable melanoma in-transit metastases (ITM). Unresectable ITM is a heterogenous disease with multiple treatment (tx) options including systemic therapies such as immune checkpoint inhibitors (ICI), regional therapies such as isolated limb infusion or perfusion (ILI/P), and intratumoral therapies such as talimogene laherparepvec (IT). Until now, there has been no direct comparison of these first-line tx for unresectable ITM. Methods: A retrospective chart review of patients (pts) with ITM treated first-line with IT, ILI/P, or ICI was performed at 11 institutions. Pts with unresectable ITM, synchronous nodal or distant metastatic disease were excluded. Results: 560 pts (54% women) were identified, 86 received IT, 353 received ILI/P, and 121 received ICI from 1990-2022. ICI pts were youngest, IT pts were oldest (p<0.001). Limb was the most common site of ITM. There was no difference in largest ITM size, but number of lesions (burden of disease (BOD)) was highest in ILI/P pts and lowest in IT pts (p=0.003). Toxicity (tox) requiring <90 days (p<0.001) or > 90 days (p=0.034) of pharmacologic tx as well as tox requiring hospitalization (p<0.001) was greatest in ICI pts. Lymphedema was more likely in ILI/P pts (p=0.016). Median follow-up was much longer for ILI/P pts at 8.0 yrs compared to 2.5 yrs for IT pts and 3.1 yrs for ICI pts. Overall response rate (ORR) was 82.2% in ILI/P pts, significantly higher than IT (72.1%, p=0.047) or ICI pts (63.6%, p<0.001). Overall survival was similar between modalities (p=0.167); however, ILI/P pts had worse progression-free survival (PFS) (p<0.0001) and melanoma-specific survival (MSS) (p=0.003). On multivariable analysis of MSS by number of ITM present, MSS remained worst if ILI/P was used for low BOD, ≤3 ITM (p=0.005), but no difference was seen between tx modalities for higher BOD, >3 ITM (p=0.211). Conclusions: ICI was used more often in younger pts with less BOD, IT in older pts with less BOD, and ILI/P in older pts with high BOD. Short and long-term tox was greater in ICI. ILI/P had the best ORR, but ICI and IT resulted in greater overall MSS. Multidisciplinary consideration of risks and benefits of each modality should guide ITM tx selection. [Table: see text]

AbstractBackgroundPrimary mesenteric soft tissue sarcomas (STS) are rare and limited evidence is available to inform management. Surgical resection is challenging due to the proximity of vital structures and a need to preserve enteric function.ObjectivesTo determine the overall survival (OS) and recurrence‐free survival (RFS) for patients undergoing primary resection for mesenteric STS.MethodsThe Trans‐Atlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG) is an intercontinental collaborative comprising specialist sarcoma centers. Data were collected retrospectively for all patients with mesenteric STS undergoing primary resection between 2000 and 2019.ResultsFifty‐six cases from 15 institutions were included. The spectrum of pathology was similar to the retroperitoneum, although of a higher grade. R0/R1 resection was achieved in 87%. Median OS was 56 months. OS was significantly shorter in higher‐grade tumors (p = .018) and extensive resection (p < .001). No significant association between OS and resection margin or tumor size was detected. Rates of local recurrence (LR) and distant metastases (DM) at 5 years were 60% and 41%, respectively. Liver metastases were common (60%), reflecting portal drainage of the mesentery.ConclusionPrimary mesenteric sarcoma is rare, with a modest survival rate. LR and DM are frequent events. Liver metastases are common, highlighting the need for surveillance imaging.

Background In this series from the Transatlantic Australasian Retroperitoneal Sarcoma Working Group (TARPSWG), the authors examined longitudinal outcomes of patients with a second recurrence of retroperitoneal sarcoma (RPS) after complete resection of a first local recurrence (LR). Methods Data from patients undergoing resection of a first LR from January 2002 to December 2011were collected from 22 sarcoma centers. The primary outcome was overall survival (OS) after second recurrence. Results Second recurrences occurred in 400 of 567 patients (70.5%) after an R0/R1 resection of a first locally recurrent RPS. Patterns of disease recurrence were LR in 323 patients (80.75%), distant metastases (DM) in 55 patients (13.75%), and both LR and DM in 22 patients (5.5%). The main subtype among the LR group was liposarcoma (77%), whereas DM mainly were leiomyosarcomas (43.6%). In patients with a second LR only, a total of 200 patients underwent re‐resection (61.9%). The 5‐year OS rate varied significantly based on the pattern of failure ( P < .001): 45.6% for the LR group, 25.5% for the DM group, and 0% for the group with LR and DM. The only factors found to be associated with improved OS on multivariable analysis were both time between second surgery and the development of the second recurrence (32 months vs 8 months: hazard ratio, 0.44 [ P < .001]) and surgery for second recurrence (yes vs no: hazard ratio, 3.25 [ P < .001]). The 5‐year OS rate for patients undergoing surgery for a second LR was 59% versus 18% in the patients not deemed suitable for surgical resection. Conclusions Survival rates after second recurrence of RPS varied based on patterns of disease recurrence and treatment. Durable disease‐free survivors were identified after surgery for second LR in patients selected for this intervention.

Abstract Background Schwannomas are rare tumours that pose a significant management challenge in the abdomen, retroperitoneum and pelvis. No data are available to inform management strategy. Methods A collaborative international cohort study, across specialist sarcoma units, was conducted to include adults presenting between 2000 and 2017 with histopathologically confirmed schwannomas within the abdomen, retroperitoneum or pelvis. Results Of 485 patients across 12 centres, 38 (7·8 per cent) were discharged without follow-up, 199 (41·0 per cent) underwent early resection and 248 (51·1 per cent) had radiological monitoring. Of these 248 patients, 96 (38·7 per cent) eventually had surgery, giving an overall resection rate of 60·8 per cent (295 of 485). At baseline, median tumour volume was 90·1 (i.q.r. 26·5–262·0) cm3. The estimated growth rate was 10·5 (95 per cent c.i. 9·4 to 11·6) per cent per year, and was consistent in the short term (within 2 years of diagnosis) and long term (beyond 2 years) (ρ = 0·405, P = 0·021). A decision to operate was more common in symptomatic patients (P &lt; 0·001) and for rapidly growing tumours (growth rate more than 20 per cent per year) (P = 0·025). R0/R1 resection was achieved in 91·6 per cent of patients (263 of 287). Kaplan–Meier long-term recurrence rates after R0/R1 resection were 2·3 and 6·7 per cent at 3 and 5 years respectively. Conclusion Specific recommendations include: indications for early surgery, prediction of growth from radiological monitoring, promotion of selective submacroscopic resection and cessation of postoperative imaging surveillance.