Blastemal predominant type Wilms tumor in Japan: Japan Children's Cancer Group.

BACKGROUND: Persistence of blastemal components after chemotherapy is a marker of poor outcome in Wilms tumor (WT). Recent reports from local Japanese areas have described pre-chemotherapy blastemal predominant type WT to also be a risk factor for relapse. The significance, however, of blastemal predominant WT remains to be evaluated in a larger study. This study retrospectively evaluated the prognostic significance of pre-chemotherapy blastemal predominant type WT in the Japan Wilms tumor Study (JWiTS) trials.

METHODS: The JWiTS trial (1996-2013) was a prospective, single-arm study. The outcomes of blastemal predominant type WT were retrospectively evaluated compared with non-blastemal type WT excluding anaplasia between 1996 and 2013. Relapse-free survival (RFS) and overall survival (OS) were estimated.

RESULTS: Of 319 primary renal tumors diagnosed by the central pathology review system, advanced stage of pre-chemotherapy blastemal predominant type WT (n = 53; 16.1%) occurred more frequently in older children than non-blastemal type WT (n = 225), and was especially frequent in female patients registered in the JWiTS trials. No significant difference in 10 years RFS and OS (78.8% vs 84.5; P = 0.201) or in 10 years RFS and OS (89.3% vs 93.5; P = 0.45) was seen between pre-chemotherapy blastemal predominant type and non-blastemal type WT.

CONCLUSIONS: Relapse-free survival and OS are not significantly different between pre-chemotherapy blastemal predominant type and non-blastemal type WT.