Treatment and outcome of patients with relapsed clear cell sarcoma of the kidney: a combined SIOP and AIEOP study

Background: Clear cell sarcoma of the kidney (CCSK) is an uncommon paediatric renal tumour. Relapses occur in about 15% of the patients. Since detailed clinical information on relapsed CCSK is scarce, the current study aims to describe outcome of patients with relapsed CCSK treated according to recent European protocols. Patients and methods: We analysed prospectively collected data of all CCSK patients who developed a relapse after complete remission at the end of primary treatment, entered onto SIOP and AIEOP trials between 1992 and 2012. Results: Thirty-seven of 237 CCSK patients (16%) treated according to SIOP and AIEOP protocols developed a relapse. Median time from initial diagnosis to relapse was 17 months (range, 5.5 months -6.6 years). Thirt-five out of thirty-seven relapses (95%) were metastatic; the most common sites of relapse were the brain (n = 13), lungs (n = 7) and bone (n = 5). Relapse treatment consisted of chemotherapy (n = 30), surgery (n = 19) and/or radiotherapy (n = 18), followed by high-dose chemotherapy and autologous bone marrow transplantation (ABMT) in 14 patients. Twenty-two out of thirty-seven patients (59%) achieved a second complete remission (CR); 15 of whom (68%) developed a second relapse. Five-year event-free survival (EFS) after relapse was 18% (95% CI: 4%-32%), and 5-year overall survival (OS) was 26% (95% CI: 10%-42%). Conclusions: In this largest series of relapsed CCSK patients ever described, overall outcome is poor. Most relapses are metastatic and brain relapses are more common than previously recognised. Intensive treatment aiming for local control, followed by high dose chemotherapy and ABMT, seems to be of benefit to enhance survival. Novel development of targeted therapy is urgently required.