Clinical features and surgical challenges of advanced retroperitoneal rhabdomyosarcoma in children: a single-center 17-year experience

Introduction

Rhabdomyosarcoma (RMS) is a common mesenchymal malignant tumor in children, accounting for 3–8% of all pediatric malignant tumors, with the head and neck, genitourinary tract, extremities, and trunk being the most prevalent sites (1-4). The primary site of origin is closely associated with prognostic outcomes. The retroperitoneum is an uncommon location for RMS and advanced retroperitoneal rhabdomyosarcoma (RRMS) is even rarer (5). Owing to the deep retroperitoneal anatomical location, these tumors typically present insidiously with strong invasiveness, leading to advanced disease at diagnosis.

Currently, there are few reports summarizing multiple cases of advanced primary RRMS. Coupled with the difficulties in surgical intervention and poor clinical prognosis, we conducted a retrospective analysis of the clinical features and prognosis of advanced RRMS (excluding primary genitourinary tract) in children. This study aims to improve clinicians’ understanding of advanced RRMS and inform prognostic optimization. We present this article in accordance with the STROBE reporting checklist (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-1-928/rc).

Methods

Patients

This study was designed as a single-center retrospective study. Clinical data of 18 pediatric patients diagnosed with pathologically confirmed RRMS at Beijing Children’s Hospital, Capital Medical University, between 2007 and 2024 were retrospectively collected. All children in this study were followed up via outpatient review and telephone. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of the Beijing Children’s Hospital (No. [2025]-E-179-R) and the family/patient informed consent requirements were waived due to the retrospective nature of the study.

Variables and data sources

Clinical staging of patients was performed using the tumor-node-metastasis (TNM) staging system (6,7), while clinical risk stratification was conducted according to the Intergroup Rhabdomyosarcoma Study Group (IRSG) classification, and adopted by the Children’s Oncology Group (COG) (6,8,9). Involvement of surrounding tissues and blood vessels by RRMS was evaluated with reference to the image-defined risk factors (IDRFs) for abdominal neuroblastoma (10). All patients underwent a comprehensive evaluation: (I) physical examination; (II) contrast-enhanced computed tomography (CT) or magnetic resonance imaging (MRI) of the head, chest, abdomen, and pelvis, as well as positron emission tomography-computed tomography (PET-CT); and (III) bone marrow aspiration to detect bone marrow involvement. Laboratory tests included complete blood count, routine chemistry panel, and urinalysis. Efficacy was assessed in accordance with the Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST v1.1), an international standard for pediatric solid tumors (11).

Bias

The retrospective design over a long period (2007–2024) with potential gaps in treatment documentation; small sample size limiting statistical power and generalizability. The children’s case management, laboratory test results, and imaging studies were reviewed by a senior clinician, a radiologist, and a laboratory technologist to minimize data errors. For pediatric patients lacking genetic test results, we established histological diagnoses of RMS subtypes based on morphological features and immunohistochemical staining (including desmin, MyoD1, and myogenin).

Study size

Due to the extreme rarity of the disease, only 17 cases of advanced RRMS were included through a single-center 17-year experience.

Inclusion criteria

Patients were included in this study if they met all the following criteria: (I) age <18 years at initial diagnosis; (II) retroperitoneal tumor location confirmed by imaging examinations (contrast-enhanced CT/MRI or PET-CT); cases with primary genitourinary tract were excluded; (III) pathologically confirmed RMS via histopathological examination; (IV) advanced-stage (IRSG III/IV with locally advanced/distant metastasis) (12); (V) cases with retroperitoneal metastatic lesions from RMS originating at other sites were excluded.

Treatment

Biopsy

Based on the initial diagnostic imaging evaluation of each patient, either needle biopsy or surgical biopsy (laparotomy or laparoscopy) was selected to ensure sufficient tissue was obtained for pathological diagnosis.

Chemotherapy

Once the pathological result was confirmed, neoadjuvant chemotherapy was initiated immediately in alternating cycles every 21 days. For intermediate-risk RRMS, alternating cycles of the VDC (vincristine + doxorubicin + cyclophosphamide) regimen and VTC (vincristine + topotecan + cyclophosphamide) regimen were administered. For high-risk RRMS, chemotherapy mainly consisted of alternating cycles of the VDC and IE (ifosfamide + etoposide) regimens. Mesna was used prophylactically for cyclophosphamide/ifosfamide to prevent hemorrhagic cystitis; routine blood tests were done, with symptomatic transfusion and colony-stimulating factors for myelosuppression.

Surgery

Every effort was made to resect all tumors without sacrificing organ function. Skeletonization of important retroperitoneal blood vessels was performed for gross total resection. Routine retroperitoneal lymph node dissection was conducted to avoid missing lymph nodes with potential metastasis.

Radiotherapy

If patients successfully passed the perioperative period, they received radiotherapy concurrently with postoperative chemotherapy. Local radiotherapy could be initiated 4–8 weeks after surgery.

Metastatic lesions

Radiotherapy was applied as the standard treatment for metastatic lesions. In highly selected patients with limited metastases, simultaneous resection of primary tumors and metastatic foci was attempted in one stage if feasible. If not, reoperation or additional radiotherapy was considered after intensive chemotherapy.

Efficacy assessment and follow-up

Imaging examinations were performed before chemotherapy and after the 2nd, 4th, and 6th courses of chemotherapy to determine the size of tumor lesions and evaluate chemotherapy efficacy. Recurrence was defined as the reoccurrence of local or metastatic tumor lesions at least 1 month after the achievement of complete response (CR) following standard tumor treatment. Overall survival (OS) was calculated as the time from the date of diagnosis to the end of follow-up or death from any cause. Event-free survival (EFS) was calculated as the time from the date of diagnosis to the occurrence of an event, where events included tumor recurrence, disease progression, or development of a second primary tumor. The follow-up period ended on August 30, 2025.

Statistical analysis

SPSS 26.0 was used for statistical processing. The variables were tested for normality; nonnormally distributed measurement data are expressed as median (interquartile range, IQR). Count data are described by percentage. The Mann-Whitney U test was applied for the comparison of non-normally distributed continuous variables between groups. Odds ratios (OR) were calculated to evaluate associations between variables. Pearson correlation coefficient (r) was used to assess the linear relationship between continuous variables. EFS and OS were analyzed by the Kaplan-Meier method and log-rank test, and survival curves were drawn. P<0.05 was considered statistically significant.

Results

Participants

After staging and grouping assessment, 17 patients were identified as having advanced RRMS and included in the final analysis. All of the included children were reviewed and confirmed as advanced RRMS by three senior pathologists.

Descriptive data

Clinical characteristics

The median age at onset was 54.0 (IQR, 31.1–72.5) months, and the median tumor size was 10.4 (IQR, 8.7–14.7) cm. Among the 17 patients, 14 (82.4%) were male and 3 (17.6%) were female. The primary symptoms included abdominal pain (n=6) and palpable abdominal mass (n=6). Other presenting symptoms were dyspnea (n=2), abdominal distension with vomiting (n=1), penile and scrotal edema (n=1), and lower extremity edema (n=1). Tumor rupture occurred in 3 patients at diagnosis: 2 cases were secondary to needle biopsy, and 1 case was spontaneous rupture. The median time from initial symptom onset to the detection of retroperitoneal lesions was 12.0 (IQR, 6.5–19.5) days. Misdiagnosis or missed diagnosis was observed in 7 patients (7/17, 41.2%) at the initial visit. The median time from misdiagnosis/missed diagnosis to the confirmation of retroperitoneal lesions was 14.0 (IQR, 7.0–120.0) days. The misdiagnosed conditions included dyspepsia (n=2), acute appendicitis (n=1), neuroblastoma (n=1), gastritis (n=1), lymphoma (n=1), and intra-abdominal infection (n=1). According to the TNM staging system, 7 patients were classified as Stage III and 10 as Stage IV. Consistent with TNM staging, the IRSG grouping identified 7 cases as Group III and 10 as Group IV. Among the 10 Stage IV patients, the most common sites of distant metastasis were distant lymph nodes (n=6), lung (n=4), bone (n=2), pleura (n=2), peritoneum (n=1), abdominal wall (n=1), brain (n=1), and cardiac-diaphragmatic angle (n=1). Detailed clinical data of the 17 patients with advanced RRMS are summarized in Table 1.

Imaging and pathological characteristics

Abdominal and pelvic contrast-enhanced CT was performed to evaluate tumor status. Morphologically, 3 tumors presented as round, while 14 showed an irregular shape. IDRFs were used to assess the relationship between tumors and surrounding organs/vessels. The most frequent involvements were as follows: abdominal aorta (n=10), iliac vessels (n=9), superior mesenteric artery (SMA) (n=6), celiac trunk (n=5), ureter (n=5), renal vessels (n=3), and spermatic cord (n=2). Detailed imaging risk factors are summarized in the Table S1. Hydronephrosis was detected by CT in 6 patients (6/16, 37.5%). At initial evaluation, 2 patients had developed post-renal renal failure, and 2 had pleural effusion. Among all cases, 16 tumors showed no internal calcifications, while cystic liquefaction was observed in 3 tumors. Figure 1 shows the imaging data of a typical case of advanced RRMS.

Figure 1 Imaging findings of a 29-month-old male with retroperitoneal rhabdomyosarcoma (Case 15). The initial tumor measured 17.4 cm × 10 cm × 10 cm. Initial abdominal contrast-enhanced CT showing a large abdominal-pelvic mass on coronal (A), sagittal (B), and horizontal (C) planes, encasing major vessels. Post-neoadjuvant chemotherapy, preoperative abdominal contrast-enhanced MRI showing tumor extent on coronal (D), sagittal (E), and transverse (F) views showed a tumor measuring approximately 4.7 cm × 5.9 cm × 6.5 cm. It exhibited slightly hyperintense T1 signal and mixed slightly hyperintense T2 signal. Post-contrast imaging demonstrated heterogeneous enhancement with patchy T1 hypointense areas showing no enhancement. The lesion continued to encircle the abdominal aorta, celiac trunk, superior mesenteric artery, and left renal artery and vein. The pancreas was displaced anteriorly. CT, computed tomography; MRI, magnetic resonance imaging.

Pathologically, 7 tumors were classified as alveolar subtype and 10 as embryonal subtype. The Ki-67 proliferation index was >20% in 10 cases. Genetic testing revealed mutations in 4 patients: 3 had confirmed FOXO1 translocation mutations (Cases 4, 14, and 16) by fluorescence in situ hybridization (FISH), 1 had a KRAS activating mutation combined with a BCOR frameshift mutation (Case 13) by next-generation sequencing (NGS).

Treatment

Of the 17 patients, 15 underwent initial biopsy (14 received neoadjuvant chemotherapy, 1 declined treatment and died); of these 14 patients, 13 had delayed surgery (12 received postoperative chemotherapy, 1 died perioperatively). The remaining 2 patients underwent primary surgery (both received postoperative chemotherapy). Among the 13 patients who underwent delayed surgery: 12 received postoperative chemotherapy, and 1 died during the perioperative period (due to thrombus formation and intestinal necrosis following vascular repair for intraoperative SMA injury). The patient was transferred to the Pediatric Intensive Care Unit (PICU) and subsequently died from multiple organ failure, Case 15). For the 12 patients who received postoperative chemotherapy, 9 further received radiotherapy, with 4 surviving and 5 dying; the remaining 3 did not receive radiotherapy, with 1 (1/3) surviving and 2 (2/3) dying. For the 2 patients who underwent immediate primary surgery at initial diagnosis, both received postoperative chemotherapy. One patient died after a second surgery (due to massive hemorrhage resulting from intraoperative injury to the external iliac artery and common iliac artery; the patient was stabilized and transferred to the PICU but subsequently died from multiple organ failure, Case 10), and the other died due to tumor progression during postoperative chemotherapy. Efficacy evaluation of neoadjuvant chemotherapy in the 14 eligible patients showed that 8 achieved partial response (PR) and 6 had stable disease (SD) (Figure 2).

Figure 2 Treatment patterns for late-stage RRMS in children. RRMS, retroperitoneal rhabdomyosarcoma.

Four patients required vascular resection/anastomosis: internal iliac artery (Case 4), thoracic aorta (Case 11), external iliac artery (Case 10), and a combination of abdominal aorta, SMA, and renal artery (Case 15). Additionally, Case 4 underwent partial ureteral resection and anastomosis.

Three patients had parenchymal organ involvement (pancreas 2, liver 1, adrenal 1, spleen 1); Case 14’s preoperative pancreatic involvement was confirmed as unrelated solid pseudopapillary neoplasm postoperatively.

Recurrence and prognostic outcomes

Six (40%) had recurrence: all local, 2 with new distant metastases (heart apex 1, right lung upper lobe 1), 1 with extensive intra-abdominal dissemination. In the recurrent patients, the median time from treatment discontinuation to recurrence was 6.4 (IQR, 4.5–19.5) months. All 6 patients with recurrence eventually died (see details in Table S1). Based on IDRFs, we divided the cohort into high-IDRFs (IDRFs >3, n=9) and low-IDRFs (IDRFs <3, n=7) groups. For local recurrence, the high-IDRFs group showed a 1.9-fold higher incidence than the low-IDRFs group, though this difference did not reach statistical significance (OR: 2.625, P=0.60). Regarding intraoperative blood loss, the high group had an average blood loss 15.9 mL higher than the low group (r=0.303, P=0.27). For vascular injury, the high group had a vascular injury rate 2.3 times that of the low group (OR: 2.8, P=0.60). Notably, the recurrent group was generally younger at onset, had larger tumors, exhibited significantly lower survival rates, and showed a higher IDRFs rate. However, none of the aforementioned variables reached statistical significance, which may be attributed to the small sample size (Table S1). In contrast, the median number of IDRFs was 4 (IQR, 2–4) in the deceased group and 2 (IQR, 1–2) in the surviving group, with a statistically significant difference (P=0.02).

Median follow-up: 117.0 (112.2–121.8) months; 12 patients (70.6%) died and 5 patients (29.4%) survived. The causes of death were as follows: 6 patients died due to disease progression after tumor recurrence; 5 died from disease progression during initial treatment (including 2 deaths from perioperative multiple organ failure); and 1 died after discontinuing treatment following biopsy. Notably, all 7 patients who had experienced misdiagnosis or missed diagnosis during initial evaluation eventually died. For IRSG stage-specific survival: 3-year EFS: IRSG III 42.9% (9.8–73.4%), IRSG IV 15.0% (1.0–45.7%) (P=0.19); 3-year OS: IRSG III 57.1% (17.2–83.7%), IRSG IV 11.7% (0.6–40.1%) (P=0.14). The combined 3-year EFS and OS rates for the entire cohort were 27.5% (12.3–61.2%) and 32.1% (15.7–65.7%), respectively (P=0.002) (Figure 3).

Figure 3 Survival curves for 17 pediatric patients with retroperitoneal rhabdomyosarcoma. EFS (A) and OS (B) for IRSG-III and IRSG-IV patients, and overall EFS and OS for all patients (C). EFS, event-free survival; IRSG, Intergroup Rhabdomyosarcoma Study Group; OS, overall survival.

Discussion

RRMS is rare and easily misdiagnosed

RMS incidence is 4.5 per million children, with a male predominance (1.3–1.5:1) (13). Consistent with this, 14/17 (82.4%) of our advanced RRMS patients were male in our study. The deep retroperitoneal location with multiple potential spaces causes nonspecific symptoms, challenging early diagnosis and increasing misdiagnosis/missed diagnosis risk. In line with this clinical dilemma, 7 cases of advanced RRMS in our study were misdiagnosed at the initial visit. Additionally, at the time of initial diagnosis, the tumors in our cohort were already large in size. Most of the patients were preschool-aged children who lacked sufficient ability to express their symptoms clearly, and the detection of the disease largely depended on parental observation of abnormal signs (such as abdominal distension or palpable mass).

Differential diagnosis

The retroperitoneum is a common location for extracranial solid tumors in children, and RRMS requires differential diagnosis from neuroblastoma, renal tumors, and pancreatic tumors. Several features may help distinguish RRMS from neuroblastoma: RRMS most commonly metastasizes to the lungs (rare in neuroblastoma); no calcification in RRMS (a hallmark of neuroblastoma) (14). This distinction may help differentiate between the two tumors. For renal tumors, contrast-enhanced CT is essential to confirm the organ of origin. Solid pseudopapillary neoplasm (SPN) of the pancreas, which occurs predominantly in adolescents, typically exhibits lower malignancy and less invasive behavior when compared to RMS. Pancreatoblastoma tends to metastasize to the liver and is often accompanied by elevated alpha-fetoprotein levels; these features aid in the differential diagnosis of advanced RRMS.

Imaging-related clinical characteristics

Hydronephrosis was common (6/16, 37.5%), closely associated with ureteral/bladder invasion: 5 with ureteral involvement and 1 with bladder involvement (all had hydronephrosis preoperatively). Therefore, the presence of hydronephrosis on preoperative imaging should heighten clinical suspicion for urinary tract involvement by the tumor.

Given the limitations of regional lymph node involvement, hematogenous metastasis, age at diagnosis, malignant tumor site, bulk, and overall histology (RHAMBO) application in advanced disease, including tumor size >5 cm, primary tumor site, local invasion and distant metastasis as common features in our study (15). Therefore, we first adapted the neuroblastoma-derived IDRFs to RRMS, justified by shared retroperitoneal origin and similar vessel/soft tissue invasion patterns, enabling effective assessment of local tumor extent. Our data showed a notable difference in IDRF scores between the mortality and survival groups: the median number of IDRFs was 4 (IQR, 2–4) in the deceased group and 2 (IQR, 1–2) in the surviving group, with a statistically significant difference (P=0.02). This finding suggests that the IDRF system may have potential applications beyond neuroblastoma, and may also be valuable for assessing intraoperative risks and stratifying prognosis in other retroperitoneal solid tumors. However, extensive prospective and multicentric studies will be required for further validation.

Treatment considerations: caution with radical surgical strategies

Fifteen (88.2%) underwent initial biopsy. Unlike retroperitoneal neuroblastoma, RMS biopsy may increase risk grouping, but it is unavoidable due to nonspecific imaging/clinical manifestations, and confirmed pathology is critical for chemotherapy selection (16). Notably, some scholars have suggested that undergoing extensive tumor resection prior to radiotherapy may benefit pediatric patients (17). However, in our study, both patients who underwent initial surgery eventually died, whereas 5 of the 15 patients who received initial biopsy followed by sequential treatment (neoadjuvant chemotherapy, delayed surgery, and postoperative adjuvant therapy) survived. This finding suggests that aggressive initial surgery for advanced RRMS should be approached with caution, as the potential risks (e.g., extensive tissue/organ injury, perioperative complications) may outweigh the benefits, especially given the advanced disease status and complex anatomical involvement.

Multimodal therapy has improved pediatric RMS 5-year survival rate from 10–20% to 70% (18). Consistent with this, our neoadjuvant chemotherapy yielded PR in 57% (8/14), controlling tumor progression, reducing volume/invasion, and improving delayed surgery feasibility.

Surgical challenges in advanced RRMS include distant metastases and extensive local organ/vessel invasion: all accessible cases were IDRF-positive; 4 required vascular repair, 1 had partial ureteral resection/anastomosis for organ preservation. A previous study has reported the feasibility of appendiceal ureteroplasty for peritoneal RMS involving the ureter (19). This procedure is primarily indicated for ureteral reconstruction when severe tumor invasion causes luminal obstruction or tissue defects, with the key goal of preserving organ function in pediatric patients. Although this specific technique was not adopted in the ureter-involved cases of our study, it highlights a critical clinical principle: individualized reconstruction strategies are necessary, tailored to tumor extent, patient age, and renal function. Such strategies must balance the need for oncological radicality (to ensure adequate tumor clearance) with the preservation of organ function (to maintain long-term quality of life in children).

Vascular invasion stands out as the primary source of surgical difficulty in RRMS, and its pattern differs distinctly from that of pediatric retroperitoneal neuroblastoma. In our study, 4 of 15 patients (26.7%) required intraoperative vascular repair. In contrast, previous reports on pediatric retroperitoneal neuroblastoma showed a much lower rate: among 129 cases, only 5 required aortic repair (20,21). Additionally, in our center’s experience with high-risk stage 4 retroperitoneal neuroblastoma over the past two years, only 14 of 84 cases (16.7%) underwent vascular repair—still lower than the 26.7% rate in our RRMS cohort (22). This discrepancy suggests that RRMS exhibits more aggressive vascular invasion, which may reflect inherent differences in the biological behavior of the two tumor types.

A notable case in our study (Case 15) illustrates the severity of vascular-related surgical risks: the patient developed SMA injury with concurrent thrombosis during surgery. Case 15 developed SMA injury/thrombosis during surgery, requiring enterostomy and parenteral nutrition but succumbing to multiorgan failure. SMA injury requires prompt management based on vascular damage and intestinal perfusion: revascularization for short-segment thrombosis, vascular replacement for severe defects, and colostomy for irreversible ischemia (with second-stage closure later) (12). This case highlights the need for multidisciplinary team (MDT) collaboration (vascular surgery, gastrointestinal surgery, and the PICU) to individualize treatment and reduce postoperative complications.

Prognosis and study limitations

Advanced RRMS has a poor prognosis: 5 survivors in our study cohort with 3-year OS of 32.1% [vs. 75% 5-year OS for localized retroperitoneal and pelvic RMS (17)]. In this study, key factors include high misdiagnosis rate (delayed treatment), advanced tumor stage, and incomplete radiotherapy as well as damage to surrounding tissues and blood vessels during surgery. Early detection, accurate diagnosis, and standardized treatment are critical (17).

Conclusions

Advanced pediatric RRMS is rare, with nonspecific symptoms and high misdiagnosis rate. Key imaging shows no calcification, and hydronephrosis suggests ureteral/bladder involvement. IDRFs assess invasion and predict prognosis. Neoadjuvant chemotherapy is effective, but surgical challenges arise from extensive vascular invasion (requiring MDT collaboration). Recurrence is prone to poor outcomes, and survival is unsatisfactory. Future studies should optimize early diagnosis, refine treatments, and expand multi-institutional data.

Acknowledgments

The authors would like to thank all patients and families participating in the study.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-1-928/rc

Data Sharing Statement: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-1-928/dss

Peer Review File: Available at https://tp.amegroups.com/article/view/10.21037/tp-2025-1-928/prf

Funding: This work was supported by the Capital’s Funds for Health Improvement and Research (CFH) (No. 2024 - 1 - 2091), and Science and Technology Program of Inner Mongolia Autonomous Region (No. 2025YFSH0002).

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://tp.amegroups.com/article/view/10.21037/tp-2025-1-928/coif). All authors report receiving funding from the Capital’s Funds for Health Improvement and Research (CFH) (No. 2024 - 1 - 2091), and Science and Technology Program of Inner Mongolia Autonomous Region (No. 2025YFSH0002). The authors have no other conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. The study was approved by the Medical Ethics Committee of the Beijing Children’s Hospital (No. [2025]-E-179-R) and the family/patient informed consent requirements were waived due to the retrospective nature of the study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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