Outcome of renal tumors registered in Japan Wilms Tumor Study-2 (JWiTS-2): A report from the Japan Children's Cancer Group (JCCG).

Background: Japan Wilms Tumor Study-2 (JWiTS-2) mandated central pathology review for all case registrations. The study aimed to compare the outcomes of patients with unilateral Wilms tumor enrolled on the JWiTS-1 and JWiTS-2 trials.

Procedure: The JWiTS-2 trial (2006-2014), a prospective, single-arm study, required compulsory submission of histologic slides to central pathology, while in the JWiTS-1 trial, such submission was not compulsory. Relapse-free survival (RFS) and overall survival (OS) versus cases in the JWiTS-1 trial (1996-2005) were statistically evaluated.

Results: Of 277 enrolled patients with primary renal tumors diagnosed by the central pathology review system, 225 patients with unilateral renal tumors were followed up over 9 years. The RFS and OS of Wilms tumor (n = 178) were 90.4% (P = 0.0003) and 96.8% (P = 0.054), respectively, as compared to 74.9% and 89.4% in JWiTS-1. RFS rates of stages I-III Wilms tumor in JWiTS-2 were more than 90%, although the outcome of stage IV Wilms tumor was significantly poorer (RFS: 66.2%) (P = 0.0094). RFS and OS of clear cell sarcoma of the kidney (CCSK; n = 31) were 82.4% (P = 0.30) and 91.3% (P = 0.42), respectively, as compared to 68.8% and 81.3% in JWiTS-1, and those of rhabdoid tumor of the kidney (RTK; n = 16) were 18.8% (P = 0.88) and 25.0% (P = 0.80), respectively, as compared to 23.5% and 23.5% in JWiTS-1.

Conclusions: RFS and OS for stages I-III Wilms tumor were improved in JWiTS-2 compared to JWiTS-1, whereas outcomes for stage IV Wilms tumor, CCSK, and RTK did not improve.