Synovial Sarcoma Is Not Associated With a Higher Risk of Lymph Node Metastasis Compared With Other Soft Tissue Sarcomas
Authors: Jacobs Andrew J. , Morris Carol D. , Levin Adam S. 
Published: April 2018

Abstract

Background
Reported rates of the incidence of lymph node metastasis in soft tissue sarcoma vary considerably. Many are based on single-institution series and small patient populations. Certain sarcoma subtypes, including synovial sarcoma, have been associated with a higher risk of lymph node involvement. Most single centers have insufficient numbers of patients to assess lymph node metastasis accurately, but larger national databases may allow a more accurate estimation.

Questions/purposes
We queried a large national database and asked the following questions: (1) What proportion of patients with soft tissue sarcoma have lymph node metastasis and distant metastasis? (2) What histologic subtypes are associated with increased risk of nodal metastasis? (3) What is the impact of lymph node metastases and histologic subtype on survival? (4) Does lymph node excision improve survival of patients with soft tissue sarcoma?

Methods
The National Cancer Institute’s Surveillance, Epidemiology, and End Results (SEER) Program is a national database that covers a geographic cross-section representing approximately 28% of the US population across demographic groups. Using the SEER database, we identified 15,525 adults diagnosed with histologically confirmed soft tissue sarcoma from 2004 to 2013. Proportions of patients with lymph node or distant metastases were calculated using descriptive statistics. Overall survival was computed using the Kaplan-Meier method. Multivariate analysis was performed using Cox proportional hazard regression to calculate the association of lymph node metastasis with overall survival while controlling for patient age, sex, race, tumor size, and tumor location.

Results
A total of 820 of 15,525 patients had lymph node metastasis at the time of diagnosis, yielding an overall proportion of 5.3% (95% confidence interval [CI], 4.9%–5.6%). Histologic subtypes that most frequently developed nodal metastasis were rhabdomyosarcoma, clear cell sarcoma, epithelioid sarcoma, and myxoid/round cell liposarcoma. Despite frequent reports regarding its association with lymph node metastasis, the proportion of patients with lymph node metastasis among 885 patients with synovial sarcoma (4.2%) was not different from the proportion with nodal metastasis in the overall soft tissue sarcoma population. For all soft tissue sarcomas, distant metastatic disease was present at diagnosis in 1869 (12%) patients (95% CI, 11.5%–12.6%). After controlling for relevant covariates, lymph node metastasis was associated with poorer overall survival (hazard ratio [HR], 1.34; 95% CI, 1.22–1.48; p < 0.001) as was distant metastasis (HR, 2.87; 95% CI, 2.66–3.09; p < 0.001). When comparing the subgroup of patients with positive lymph nodes, lymphadenectomy in conjunction with local excision/limb salvage was associated with the highest overall 5-year survival (HR, 0.46; 95% CI, 0.31–0.67; p < 0.001).

Conclusions
In clarifying the overall proportion of patients with soft tissue sarcoma with nodal metastases, the current study indicates that lymph node metastases occur at a higher proportion than previous studies have suggested and that synovial sarcoma is not associated with a higher risk of lymphatic spread compared with soft tissue sarcoma overall. Patients with lymph node metastases are associated with poorer survival than those without metastases. Further investigation is needed to clarify the apparent improved overall survival after lymphadenectomy in the setting of nodal metastasis from soft tissue sarcoma.

Level of Evidence
Level II, prognostic study.