Molecular profiling of solid tumors is increasingly essential in oncology practice, guiding diagnosis-prognosis and providing patients with access to molecularly matched therapies that can improve outcomes. In this study, 554 patients with advanced solid tumors were evaluated through the POWER (Precision Oncology at Western University) study, a first of its kind Canadian study, designed to prospectively assess the clinical impact of expanded pan-cancer next-generation sequencing (NGS) panel testing on patient management, in real-world oncology practice and evaluate the overall health system impact. The findings reveal that 79% of patients had clinically relevant variants, and nearly 28% experienced changes in treatment eligibility because of the identification of novel druggable mutations. Additionally, the analysis shows that a pan-cancer NGS panel significantly impacted patient management, with 18% of patients receiving access to clinical trials and off-label therapy with expected better outcomes and 19% (31/162) patients, previously tested by tumor-specific panels, experiencing management changes when tested through POWER. This study also highlights the broader health system impact: access to safer treatment options (14.5%), change in management (17.6%), treatment sequence changed (17.3%), and Ministry of Health formulary treatment saved (12.5%). These results underline the benefits of expanded NGS testing over tumor-specific panels in guiding personalized treatment decisions, optimizing patient care, and enhancing health care delivery in oncology.

There is a paucity of data on the utility of a second prostate-specific membrane antigen (PSMA) PET/CT scan after an initial negative scan in patients with recurrent prostate cancer. The purpose of this study was to assess the utility of a second PSMA PET/CT scan in these patients. Methods: This cohort comprised patients in the PSMA PET Registry for Recurrent Prostate Cancer in Ontario, Canada, who were recruited in 1 of 6 predefined clinical cohorts between October 2018 and September 2022 who had more than 1 PSMA PET/CT scan and whose initial scan was negative. The scan positivity rate, serum prostate-specific antigen (PSA), PSA doubling time, and management change were compared with baseline data. Results: In total, 210 of the 4140 patients in the registry fulfilled the inclusion criteria for the current analysis. The positivity rate of the second PET scan was lower than the baseline PET scan (56.2% [118/210] vs. 68.4% [2832/4140], P = 0.0002). Detection rates were higher in patients with elevated serum PSA (66.9% [107/160] for PSA of 0.5 ng/mL) and a PSA doubling time of less than 12 mo (64.7% [75/116]). Although differences in disease distribution (locoregional vs. distant) were not significant, visceral metastases were more common on the second PET scan (8.5% [10/118] vs. 2.2% [62/2832], P = 0.00002). Management change after a second PET scan was less frequent but remained high (46.4% [83/179]), with more frequent change to salvage therapy for extrapelvic metastases (11% [23/210] vs. 7.3% [302/4140], P = 0.0492). Conclusion: More than half of patients with biochemical failure after primary therapy for prostate cancer who have an initial negative PSMA PET/CT scan may have disease identified on a second PSMA PET/CT scan. The impact of a second PSMA PET/CT scan remains high, with management change necessary for nearly 50% of patients. A second PSMA PET/CT scan after an initially negative scan is more likely to be informative among patients with a PSA greater than 0.5 ng/mL or a PSA doubling time of less than 12 mo.

5019 Background: The PLUDO trial randomized patients with mCRPC to receive either LuP or DOC, with cross-over permitted at radiographic progression (RP). At the primary analysis, there was no significant difference in the primary endpoint of 1 st line radiographic progression free survival (rPFS) (HR 1.01, 90% CI: 0.77, 1.31). However, overall survival (OS) was in favor of patients randomized to receive docetaxel first (HR 1.64, 95% CI: 1.14, 2.35) (KN Chi, et al. ESMO Congress, 2025). To provide insights into potential reasons for the survival difference, we report the prespecified secondary objective of rPFS after cross-over therapy. Methods: Multi-centre open-label randomized phase II trial. 199 patients with chemotherapy-naïve, PSMA-PET positive mCRPC progressing after ARPI therapy were randomized 1:1 to receive either LU-P 7.4 GBq IV q6 weeks or DOC 75 mg/m2 IV q3 weeks, with cross-over permitted at progression. rPFS2 was measured from randomization to RP or death after cross-over therapy, “2 nd line rPFS” was from time of start of cross-over therapy to RP or death, OS was defined from time of initial randomization to death, and “2 nd line OS” was from time of cross-over therapy to death. Results: 159 patients had an rPFS event on 1 st line therapy (LuP: n = 79, DOC: n = 80) including 24 deaths (LuP: n = 16, DOC: n = 8). At the time of 1 st rPFS, there were no substantive differences between arms for grade 3-4 adverse events, but patients on LuP reported better quality of life (FACT-P). Of the 135 patients alive, 104 received cross-over therapy (LuP → DOC: 42, DOC → LuP: 62). There were no clinically relevant differences in baseline characteristics of patients who had cross-over therapy between treatment arms. OS was worse for patients that did not cross-over compared to those who did cross-over (LuP arm: HR 3.18 (95% CI 1.93, 7.42); DOC arm: HR 4.73 (95% CI 1.96, 11.38)). For the 104 patients who received both lines of therapy, there was no differences in efficacy outcomes for 2 nd line rPFS, rPFS2, OS, or 2 nd line OS (TABLE). PSA decline ≥ 50% was higher with cross-over Doc than LuP (69% vs 40%, P = 0.004). There were 9 grade 3 adverse events related to cross-over therapy in each arm. Conclusions: In the PLUDO study, there was no difference in first-line or cross-over rPFS between LuP and DOC. In patients who received cross-over therapy, this analysis shows no OS difference, suggesting that imbalance in cross-over from LuP to Doc likely impacted the OS difference in the ITT population and emphasizes the importance of both treatments on efficacy outcomes. Clinical trial information: NCT04663997 . LuP → DOC(median, months)n = 42 DOC → LuP(median, months)n = 62 HR(DOC → LuP/LuP → DOC) 2 nd line rPFS 4.8 5.4 0.86 (90% CI: 0.58, 1.26) rPFS2 18.5 15.8 0.91 (90% CI: 0.61, 1.35) 2 nd line OS 8.1 8.3 0.94 (95% CI: 0.53-1.64) OS 23.2 20.0 0.88 (95% CI: 0.50, 1.53)

PURPOSE:Advances in imaging have enabled identification of intraprostatic GTVs, creating opportunities for micro-boosting in prostate radiotherapy. However, variability exists in patient selection, target delineation, and treatment planning. This study aimed to characterize expert contouring variability and establish consensus guidance for GTV micro-boosting using a contour-based modified Delphi consensus. METHODS:International radiation oncologists with expertise in GTV micro-boosting participated in a two-part study comprising a contouring exercise and a two-round modified Delphi consensus. Participants contoured GTVs on two prostate cancer cases with mpMRI and PSMA-PET imaging, including one complex case with imaging discordance. Contouring agreement was assessed using Fleiss' kappa, intraclass correlation coefficients (ICC), and STAPLE analysis. Subsequently, participants completed iterative Delphi surveys addressing patient selection, imaging requirements, contouring practices, and treatment planning. Consensus and strong consensus were predefined as ≥75% and ≥90% agreement, respectively. RESULTS:Fifteen of 20 invited experts completed the study. Contouring agreement was high in the simpler case but substantially lower in the complex case. PSMA-PET-based GTVs were consistently larger than mpMRI-based GTVs. Overall, consensus or strong consensus was achieved for 43 of 131 statements (33%). Agreement was reached on key aspects of GTV delineation, including use of combined T2 and DWI/ADC sequences on mpMRI, eligibility of PI-RADS 4-5 and PROMISE 4-5 lesions for boosting, preferred use of PSMA-targeted tracers, and avoidance of CTV margins when PET and MRI information are used in combination. No consensus was achieved on SBRT micro-boosting outside clinical trials, margin expansion using single-modality imaging, or optimal dose prescriptions to the GTV or uninvolved prostate. CONCLUSION:This contour-based modified Delphi study demonstrates variability in GTVs delineation for complex cases and identifies areas of expert consensus that can inform standardized implementation of prostate GTVs micro-boosting.

BACKGROUND:Prostate-specific membrane antigen (PSMA)-PET usage in patients with prostate cancer is growing rapidly. Thus, novel risk-group definitions based on PSMA-PET are urgently needed for guidelines, clinical use, and trial study design. We report improved risk classification based on PSMA-PET Prostate Cancer Molecular Imaging Standardized Evaluation (PROMISE; PPP) nomograms (PPP3) to prognosticate 3-year, 5-year, and 7-year overall survival. METHODS:In this international, retrospective, registry-based cohort study, we collected data from the PROMISE PET registry with ongoing overall survival follow-up. Male patients (aged ≥18 years) with histological proven prostate cancer at any disease stage and any performance status, who underwent any PSMA-PET between Dec 6, 2012, and June 26, 2024, were included in the registry. Patients with neuroendocrine pattern or metastasised or disseminated malignancy other than prostate cancer were excluded. 35 investigator sites in Europe, Asia, Australia, North America, and South America were split pairwise (2:1) into development and validation cohorts. Entire investigator sites were split pairwise according to their site characteristics (ie, number of patients per disease group, country, follow-up). The primary study objective was overall survival. PPP3 nomograms were created based on Cox regression models with least absolute shrinkage and selection operator penalty to prognosticate 3-year, 5-year, and 7-year overall survival. Calibration curves and Harrell's c indices were applied and head-to-head comparison with clinical risk scores separated for each disease subgroup was conducted. Based on the visual PPP3 nomogram, a simplified risk-stratification table was created. FINDINGS:We analysed 11 154 patients and 7253 were included in the development cohort and 3901 in the validation cohort. Median follow-up to censoring or death was 4·9 years (IQR 3·5-6·6). Clinical disease group and PROMISE metrics were combined into visual and quantitative PPP3 nomograms, respectively. C indices were 0·83 (95% CI 0·82-0·84) for the visual nomogram and 0·84 (0·82-0·85) for the quantitative nomogram. Both nomograms and the simplified risk stratification table were accurate and equal or superior compared with established clinical risk scores (International Staging Collaboration for Cancer of the Prostate, European Association of Urology, a nomogram defined by Gafita and colleagues, and National Comprehensive Cancer Network). INTERPRETATION:We present new risk nomograms by PROMISE along with a simple table to prognosticate 3-year, 5-year, and 7-year overall survival in prostate cancer. PROMISE and PPP3 assessments are freely available online for global implementation. FUNDING:German Research Foundation, Prostate Cancer Foundation, Innovative Health Initiative Joint Undertaking, Novartis, AstraZeneca, and Amgen.

BACKGROUND AND OBJECTIVE:The PROFIT trial was designed to compare moderately hypofractionated (HF) radiotherapy versus conventional fractionation (CF) for patients with intermediate-risk prostate cancer (IR-PC). Similar efficacy and toxicity outcomes were previously reported. The aim of the current analysis was to evaluate differences in long-term patient-reported outcomes (PROs) between the HF and CF arms in PROFIT. METHODS:For the PROFIT phase 3 randomized clinical trial, patients with IR-PC (n = 1206) were enrolled from 14 sites in Canada, 12 in Australia, and one in France and randomized to receive 78 Gy in 39 fractions over 8 wk (CF) or 60 Gy in 20 fractions over 4 wk (HF). PROs were evaluated at baseline and 24 and 48 mo using the Expanded Prostate Cancer Index Composite, American Urological Association Symptom Score (AUASS), and the 12-item Short Form Health Survey (SF-12) comprising a physical component summary (PCS) and a mental component summary (MCS). A minimally important difference (MID) was defined as a deterioration in domain- or subdomain-specific health-related quality of life (HRQoL) score by ≥0.5 times the standard deviation at each time point in comparison to baseline. Statistical significance was set at p < 0.01. KEY FINDINGS AND LIMITATIONS:AUASS results were similar and stable over time in both arms (median 5 points, interquartile range 2-9; p > 0.2). There were no significant differences in scores for urinary, bowel, sexual, and hormonal domains or subdomains between the arms at any time point (p > 0.02). The greatest decline over time occurred in sexual domain, with a decrease of ≥10 points from baseline to 24 mo in both arms. SF-12 mean scores for both PSC and MSC were similar in the two arms and remained stable at all time points. The only significant differences in the proportion of patients reporting MIDs were for the bowel subdomains at 48 mo, with significant MID reductions favoring HF for both the bowel summary score (53% vs 44%; p = 0.01) and bowel function score (51% vs 39%; p = 0.001). Overall treatment satisfaction was high in both arms: ≥88% of patients were either satisfied or extremely satisfied with their treatment. CONCLUSIONS AND CLINICAL IMPLICATIONS:PRO results from the PROFIT trial suggest no significant differences in urinary, bowel, sexual, hormonal, and general HRQoL between CF and HF radiotherapy schedules. This study provides level 1 evidence supporting the use of moderate HF radiotherapy as standard treatment in patients with IR-PC. This trial is registered on ClinicalTrials.gov as NCT00304759.

BACKGROUND:In the treatment of metastatic castration-resistant prostate cancer (mCRPC), the standard radionuclide 177Lu (β⁻ emitter) is being challenged by alternatives, particularly the α-emitter 225Ac and Auger electron emitter 161Tb, due to their superior radiobiological properties. These include higher linear energy transfer (LET) and shorter ranges, which enhance localized cell killing while minimizing off-target effects. While these radionuclides induce DNA damage both in source-cells and neighboring cells (crossfire effect), their distinct radiation profiles provide critical metrics to compare their therapeutic efficacy. By quantifying these differences, especially in micrometastatic settings, the optimal radionuclide for specific clinical scenarios could be selected. PURPOSE:This Study aims to develop a comprehensive pipeline based on Monte Carlo (MC) simulations to compare the therapeutic efficacy of 225Ac, 177Lu, and 161Tb in the treatment of mCRPC based on clinically administered activity (7.4 GBq for 177Lu, 161Tb, and 7 MBq for 225Ac) in a multi-cell model. Besides evaluating the absorbed dose at the cellular level, the Biological Effect Cell Kernel (BECK) method is proposed to compare the radiobiological effect of radionuclides, accounting for the crossfire effect using 3D convolution. METHODS:A 2 µm resolution cell model was constructed with a 20 µm cell, an 8 µm nucleus diameter, and a 26 µm center-to-center distance. This configuration resulted in a cellular fraction of 0.24 mL/g, in agreement with that estimated from six prostate cancer patients using CT Perfusion. The prostate time-integrated activity (TIA) in the model was estimated from a patient based on a dynamic 300 MBq 18F-DCFPyL PET scan after scaling to account for the higher administered activity in therapy. The TOPAS-nBio MC tool was used to calculate the absorbed dose and the DNA breaks in the cell model. To account for the crossfire effect, we created the BECK, an isotropic 3D kernel, demonstrating the DNA breaks in the source-containing cell, and those induced in its neighboring cells. The BECK was convolved with the 3D TIA maps of the cell model to obtain the DNA break maps. RESULTS:The cellular absorbed dose was higher than the macro-scale dose based on SPECT-derived TIA, by 31.3%, 15.7%, and 39.8% for 225Ac, 177Lu, and 161Tb, respectively. At the single-cell level, 225Ac induced markedly higher DNA breaks per source - 48 double-strand breaks (DSBs), and 32 complex DSBs, compared to 177Lu - 0.022 and 0.017, and 161Tb - 0.083 and 0.073, respectively. Crossfire effects were dominant for 255Ac and 177Lu at ∼75% and less pronounced for 161Tb at ∼41%. The maximum ranges at which 99.99% of the total DNA breaks were observed were approximately 85 µm for 225Ac, 150 µm for 177Lu, and 110 µm for 161Tb. CONCLUSIONS:DPKs and BECKs of 2 2⁵Ac, ¹⁷⁷Lu, and ¹⁶¹Tb were developed to quantify cellular-level dose distributions and biological efficacy, revealing micrometer-scale heterogeneity accentuated by short-range emissions (α, CEs, AEs). Results demonstrate ¹⁶¹Tb's optimal performance for micrometastases-surpassing ¹⁷⁷Lu's efficacy with lower toxicity than 2 2⁵Ac-while relative biological effectiveness predicts activity requirements: 2 2⁵Ac << ¹⁶¹Tb < ¹⁷⁷Lu.

35 Background: PREP was initiated in Ontario to provide access and characterize performance of PSMA PET CT among men with recurrent prostate cancer after primary definitive treatment (RP or RT). Methods: Between 03/18 and 09/22, 4135 men were accrued. Men were enrolled and imaged with 18F-DCFPyL at 1 of 6 participating sites within 1 of 6 clinical cohorts. Standardized reports delineated sites of recurrence and post PET management changes. Linkage to provincial databases allowed estimation of overall survival and utilization of salvage radiotherapy after PET. Results: Median follow-up was 1.8 years; key findings are in Table 1. Significant predictors of a positive PET scan on multi-variable analysis included: higher PSA at time of PET and clinical cohort (highest for cohort 4). Significant predictors of change in management were type of recurrence (highest for loco-regional) and higher PSA. Significant predictors of worse overall survival included clinical cohort (worst for cohort 4), extent and type of metastases (worst for mixed bone/lymph/visceral or extensive metastases). A change in management post PET was a significant predictor of improved survival. Conclusions: The PREP registry facilitated access to PSMA PET/CT with high rates of disease detection and impact on management. Significant factors associated with survival were extent and sites of disease detected and management change after PET. Clinical trial information: NCT03718260 . PREP registry: Key findings. Total (n=4135) Cohort 1 (n=255): BF within 3 months from RP and pN+ or PSA >0.1 Cohort 2 (n=1500): BF following RP Cohort 3 (n=1040): BF post RPand adjuvant or salvage RT Cohort 4 (n=263): BF while on salvage hormone therapy Cohort 5 (n=176): BF following Therapy for Oligo-metastases on prior PET Cohort 6 (n=901): BF following primary RT Median Age at scan (IQR) 71.0 (66.0–76.0) 66.0 (61.0–70.0) 70.0 (65.0–74.0) 72.0 (67.0–76.0) 74.0 (69.0–79.0) 73.0 (66.0–77.0) 75.0 (70.0–79.0) Median PSA (IQR) at scan (ng/mL) 1.3 (0.3–4.0) 0.7 (0.2–2.5) 0.3 (0.2–1.0) 1.1 (0.5–2.7) 3.5 (1.6–7.2) 2.4 (1.0–5.3) 4.4 (3.1–7.4) PET: Negative Findings 1216 (29.4) 84 - 88 (32.9 - 34.5)* 749 (49.9) 258 (24.8) 19 (7.2) 18 - 22 (10.2 - 12.5)* 84 (9.3) PET: Locoregional Recurrence 1377 (33.3) 95 (37.3) 471 (31.4) 295 (28.4) 63 (24.0) 34 (19.3) 419 (46.5) PET: Oligo-Metastatic (≤5 metastases) 1021 (24.7) 45 (17.6) 224 (14.9) 354 (34.0) 111 (42.2) 70 (39.8) 217 (24.1) PET: Extensive Metastases 521 (12.6) 29 (11.4) 56 (3.7) 133 (12.8) 70 (26.6) 52 (29.5) 181 (20.1) Change in management post PET 2070 (50.1) 135 (52.9) 585 (39.0) 552 (53.1) 152 (57.8) 99 (56.3) 547 (60.7) Radiotherapy within 6 months 1729 (41.8) 165 (64.7) 866 (57.7) 346 (33.3) 88 (33.5) 49 (27.8) 215 (23.9) Died during follow-up period 138 (3.3) 1 - 5 (0.4 - 2.0)* 18 (1.2) 30 (2.9) 35 (13.3) 8 -12 (4.5 - 6.8)* 44 (4.9) BF: Biochemical Failure; RP: Radical Prostatectomy; RT: Radiotherapy; IQR: Interquartile Range. *Small cell size.

PurposeTheranostics integrates diagnostic imaging (e.g., 18F-PSMA-1007 PET) with targeted radioligand therapy (TRT; e.g., 177Lu-PSMA-617), but personalized dosimetry remains challenging due to complex dose calculations. Current methods like Monte Carlo simulations are accurate but require impractical post-treatment multi-day SPECT/CT imaging. Here we establish a proof-of-concept framework using pre-treatment PET/CT to predict TRT doses via graphical analysis and Monte Carlo modeling, eliminating the need for serial imaging. Our voxel-based approach demonstrates significant dose variations in prostate cancer patients under standard TRT with a one-size-fits-all radioligand dose, enabling pre-treatment dose personalization—a critical step toward precision radiotheranostics.MethodsDynamic PET/CT scans obtained with 18F-DCFPyL over 22 min from six prostate cancer patients were used in this study. Tissue time-integrated activity (TIA), that is, the total number of decays from the accumulated radioligand, was calculated as the product of the area under the curve (AUC) of an extrapolated arterial time activity curve (TAC) and the Logan distribution volume (LDV) determined by graphical analysis of tissue TAC. The resulting 177Lu-PSMA-617 TIA map, along with the CT-derived tissue geometry, density, and composition maps, were used to calculate the absorbed dose in the prostate tumor, overall prostate, and bone marrow in the femurs by egs_mird, a Monte Carlo-based absorbed dose calculation. Biological effective dose (BED) was calculated using the voxel-based absorbed dose and an extended radiobiological linear quadratic model accounting for dose rate, DNA repair, and clonal repopulation.ResultsVoxel-wise LDV graphical analysis demonstrated strong linearity, with an interpatient mean R2 of 0.999973 ± 0.000047 (mean ± SD). Using a one-size-fits-all radioligand dosing approach, significant variations in absorbed dose were observed: 10.4 ± 4.9 Gy/GBq in tumors, 5.1 ± 0.7 Gy/GBq in normal prostate tissue, and 1.0 ± 0.3 Gy/GBq in bone marrow. These variations were influenced by differences in both LDV and arterial TACs among the patients—the former due to radioligand binding avidity and the latter to tumor burden and clearance rates.ConclusionWe developed a framework for personalized TRT dose calculations using pre-treatment diagnostic PET/CT scans, eliminating the need for post-treatment SPECT/CT scans via the LDV-based method. This approach addresses variability in tumor and organ-at-risk doses from one-size-fits-all radioligand dosing, enabling optimized pre-treatment planning and integration with external beam radiation therapy (EBRT) or brachytherapy, if indicated, for precise and effective therapy. This method shows promise but requires further validation through larger studies and direct comparison with post-treatment dosimetry to confirm its accuracy.

INTRODUCTION: Prostate-specific membrane antigen-positron emission tomography (PSMA-PET) is a new standard for the imaging of high-risk or recurrent prostate cancer. While marginalization disparities exist for prostate cancer, less is known in the context of PSMA-PET. The objective of the study was to determine if marginalization was associated with access, PET positivity, management change, radiation use, and survival of prostate cancer in a universal healthcare system. METHODS: Patients enrolled in the Ontario PSMA-PET Registry for Recurrent Prostate Cancer (PREP) between 2018 and 2022 were included. The Ontario Marginalization Index (material resources, racialized/newcomer, age/labor force, household/dwellings) was used. Outcomes included access, PET positivity, management change, radiation use, and survival. Cox proportional hazards and logistic regression models examined the association between marginalization and outcomes. Provincial administrative databases were leveraged to generate a diagnosis and a survivorship cohort of prostate cancer patients who received primary treatment to compare with the PSMA-PET cohort. RESULTS: There were 4034 patients in the PSMA-PET cohort. Patients at higher material marginalization quintiles were under-represented in the PSMA-PET Registry Database. Similar under-representation was noted in the diagnosis (n=123 128) and survival (n=56 753) cohorts. Within the PSMA cohort, marginalization dimensions were not significantly correlated with PET positivity, management change, or radiation use. CONCLUSIONS: Marginalization quintiles across PSMA-PET access were similar in distribution to prostate cancer diagnoses and survivor cohorts. We found no association of marginalization with PET positivity, management change, or radiation use among those receiving PSMA-PET.

Introduction: Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma among children in North America. Early diagnosis and treatment are important to prevent disease progression and improve prognosis. Case presentation: A 6-year-old-boy presented with a 1cm perianal lesion that was tender and erythematous. Presumed diagnosis was perianal abscess: incision & drainage was performed and complicated with significant bleeding requiring arterial embolization. Previous computed tomography (CT) had reported a large abscess cavity. Significant growth of tissue at surgical site and swelling of the right buttock and perineal area prompted further imaging with MRI which demonstrated suspicion for a pelvic soft tissue mass with extension to the perineum. Biopsies confirmed the mass was an embryonal rhabdomyosarcoma (RMS). He was diagnosed with intermediate risk Group III, Stage III translocation-negative rhabdomyosarcoma. He was treated with VAC/VI. Discussion at province-wide tumor boards recommended no further resection given the inability to achieve negative margins. The patient underwent proton beam therapy for local control. There was reduction in size of the pelvic mass, the perineal wound healed, and the defect completely resolved while on active therapy. The patient remains well now eight months into active follow up. Conclusion: Perineal RMS is a rare disease and difficult to diagnosis as it often presents very similarly to perianal abscess. While it is not reasonable to screen all painful perianal masses with MRI, reflection of this case demonstrates some delineating features that can be useful to suggest an alternative diagnosis in order to minimize morbidity and shorten time to diagnosis.

Pediatric central nervous system (CNS) tumors are often classified by distinct histologic and molecular features; however, some tumors remain unclassified, resulting in diagnostic and therapeutic challenges. We report a case of a previously healthy 3-year-old female who presented with right eyelid ptosis and headache. Imaging revealed a right middle cranial fossa mass. Following surgery and histopathologic and molecular analyses, the diagnosis was a malignant neoplasm with mixed neural and myoblastic differentiation, not elsewhere classified based on the current World Health Organization (WHO) classification. We describe a unique hybrid treatment approach for this rare tumor consisting of rhabdomyosarcoma and embryonal treatment regimens.