Lymph node metastases in non-rhabdomyosarcoma soft tissue sarcoma

Background: Lymph node metastases in non-rhabdomyosarcoma soft tissue sarcoma (NRSTS) are uncommon in pediatric patients. Previous studies suggested that the pattern of lymph node involvement in pediatric patients was similar to adult patients in NRSTS, indicating that patients with epithelioid sarcoma and clear cell sarcoma have increased incidence of lymph node involvement at initial diagnosis. Hence, in order to further understand the pattern of lymph node involvement among pediatric patients with NRSTS, we analyzed data from a large cohort study (ARST0322), which represented the largest prospectively treated cohort of pediatric NRSTS patients in the U.S. It offered us opportunity to further study the characteristics and survival outcomes for NRSTS pediatric patients. ❧ Methods: The target population consisted of 551 patients aged less than 30 years old, all of whom had met the eligibility requirements and received a novel risk-based treatment. Our study population was the patients with lymph node metastases (in total 22 people). Fisher’s exact test and two-sample t-test were used to describe demographics and tumor clinical features between lymph node metastases patients and non-lymph node metastases patients. Kaplan–Meier survival plots with log-log transformed confidence intervals and log-rank test stratified by presence or absence of distant metastases were used to evaluate event-free survival and overall survival. Finally, Cox proportional-hazard regression was performed to select potential risk factors for EFS and OS for lymph node metastases patients. ❧ Results: Synovial sarcoma (6 cases) and epithelioid sarcoma (5 cases) were the most frequent histotypes among NRSTS pediatric patients with lymph node involvement. Lymph node metastases pediatric patients had significantly larger maximum diameter tumor size [mean (SD) 11.2 (6.3) cm] compared to patients without lymph node involvement [7.6 (5.3) cm, Two-Sample T-Test: p=0.0020]. During mean 4.6 (1.7) years of follow up time, the 5-year event-free survival (EFS) and overall survival (OS) for pediatric patients without lymph node metastases and distant metastases were 75.8% ± 2.1% and 86.4% ± 1.8%, respectively. For pediatric patients with both lymph node metastases and distant metastases, the EFS and OS were both 16.7% ± 10.8%. We found presence of distant metastases at diagnosis was a strong risk factor for event-free survival and overall survival among lymph node pediatric patients, and presence of lymph node metastases at diagnosis was an independent risk factor from presence of distant metastases for overall survival among all patients. ❧ Conclusions: Pediatric patients with NRSTS lymph node involvement had different tumor size and survival outcomes compared to patients without lymph node metastases. Moreover, presence or absence of lymph node metastases only showed significant difference in overall survival among all pediatric patients. We suggest lymph node involvement play an important role in the failure of overall survival even in the presence of distant metastases.