Clinicopathological analysis of retroperitoneal solitary fibrous tumours: a study of 31 cases.

A solitary fibrous tumour (SFT) is a mesenchymal tumour that exhibits fibroblast differentiation and rarely occurs in the retroperitoneum. The main purpose of this study was to explore the clinical manifestation, histopathological features and biological behaviour of retroperitoneal SFT. From 2011 to 2020, 31 patients were hospitalized and diagnosed with retroperitoneal SFTs. We summarized and analysed the morphological features, immunophenotype, treatment and prognosis. Patients (13 M; 18 F) ranged in age from 25 to 79 years with a mean age of 53.6 years. The main symptoms included an abdominal mass (48.4%) and abdominal discomfort (25.8%). The mean maximum diameter of the tumours was 12.9 cm (range, 4-40 cm). Histopathologically, there were 17 classic cases and 14 hemangiopericytoma-like cases. The tumour cells were positive for STAT6 (96.8%), CD34 (96.8%), CD99 (93.5%) and BCL-2 (90.3%). All patients were treated with complete surgical excision, and 3 of the patients also received chemotherapy. After a median follow up period of 44 months (range, 6 to 107 months), 2 patients died. Patients in the high- or intermediate-risk group were prone to metastasis and/or recurrence. The sites of metastases and/or recurrences involved the liver, bone and pelvis. The Ki-67 labelling index in the high-intermediate risk group (median, 10%) was significantly higher than that in the low-risk group (median, 3%). The retroperitoneal SFT demonstrates an indolent clinical course, and patients from the high- or intermediate-risk group require close follow-up. A Ki-67 labelling index ≥10% may be used as an important reference for prognosis.