Epidemiology and Outcomes of Retroperitoneal Sarcoma: An Analysis of the Population-Based Cancer Registry in Japan 2016-2019.

Background: Retroperitoneal sarcoma (RPS) is a rare cancer, so few reports have previously characterized its national profiles. The capture rate of RPS in the Bone and Soft Tissue Tumor Registry was only 20%. The present study aimed to clarify the characteristics and clinical outcomes of RPS using the National Cancer Registry (NCR), which contains nationwide population-based data from Japan.

Methods: We analyzed data from 20,079 patients with soft-tissue sarcomas (STS), entered into the NCR in 2016-2019 using the International Classification of Diseases-Oncology, Third Edition cancer topography and morphology codes. We extracted demographics (sex, age), tumor details (tumor location, histology, extent of disease), treatment, and prognosis for each patient.

Results: Of the 20,079 patients, 3311 patients were diagnosed with RPS. RPS accounts for 16.5% of all STS, with an adjusted incidence of 0.41/100,000/year. Of patients with RPS, 70.9% were aged 60 years or older and 52.7% were at the 'regional' stage at the time of diagnosis. Surgery was performed in 70.0% of cases, while chemotherapy and radiotherapy were performed in only 21.5% and 8.3% of cases, respectively. The 3-year overall survival (OAS) of the RPS patients was 57.3%. The multivariate analyses showed that of the 3,311 patients with RPS, worse OAS was associated with being male, older age, a histology of undifferentiated pleomorphic sarcoma/malignant fibrous histiocytoma, cancer discovery other than by cancer/health screening, being treated at low-volume hospitals, advanced disease, and not having surgery.

Conclusions: The present study is the first to have clarified the epidemiology, clinical features, treatment, prognosis, and significant factors affecting prognosis of patients with RPS in Japan.

Level of evidence: Level Ⅲ, prognostic studies.