Soft tissue sarcoma: the predominant primary malignancy in the retroperitoneum.

Purpose. In the clinical work-up of a retroperitoneal mass, the diagnosis of soft tissue sarcoma is often not considered. Incidence rates of various malignant and benign retroperitoneal tumours were studied to determine the incidence of soft tissue sarcoma in comparison with other neoplasms in the retroperitoneal space.Method. Nation-wide data on retroperitoneal tumours, collected prospectively over a 5-year period (1 January 1989- 1 January 1994), were supplied by the Netherlands Cancer Registry and The Dutch Network and National Database for Pathology.Results. Seven hundred and six patients with a primary retroperitoneal neoplasm were identified; 566 patients had a malignant tumour (80%). A soft tissue sarcoma (STS) was the most frequently diagnosed malignant tumour (n = 192), The agestandardised incidence of retroperitoneal STS was 2.5 per million person-years. The male/female ratio for STS was 0.73. In females, STS comprised 41%of all malignant retroperitoneal tumours, carcinoma of unknown primary tumour site (CUP) comprised 31%, and malignant lymphomas (ML) comprised 22%, whereas in males these values were 28% (STS), 30% (CUP), and 32% (ML), respectively.Discussion. Soft tissue sarcomas, albeit rare, are relatively common primary tumours in the retroperitoneum, especially in women.