Microscopic neoplastic thrombosis in localised nephroblastoma: does it influence outcome?

INTRODUCTION: Microscopic neoplastic thrombosis (MNT) is reported to occur frequently in Wilms tumour (WT). The aim of this study is to determine whether MNT influences prognosis in localised WT. PATIENTS AND METHODS: Records and slides of 80 consecutive, unselected, localised WT patients were retrospectively reviewed. All patients received chemotherapy before surgery according to SIOP Protocol. The median follow-up was 9 years (range 0.5-25.8). The Kaplan-Meier method and the Cox proportional hazard model were applied. RESULTS: MNT was present in 14 (18%) cases. Out of 14 patients with MNT, 6 presented macroscopic thrombosis and 5 had either blastemal predominance or anaplastic histology. The 5-year overall survival (OS) and progression-free survival (PFS) for the whole population were 95% (95% confidence interval, CI, 87-98%) and 91% (95% CI 82-96%), respectively. The 5-year OS and PFS for MNT positive patients were 92% (95% CI 57-99%) and 77% (95% CI 44-92%), while the 5-year OS and PFS for MNT negative patients were 96% (95% CI 87-99%) and 94% (95% CI 85-98%), respectively; the difference was statistically significant (p<0.05) for PFS. In multivariate analysis, only the presence of anaplasia retained significance with a hazard ratio (HR) of 14.8 and 12.9 (p<0.05) for recurrence and death, respectively. CONCLUSION: These data suggest that the presence of MNT increases the risk of recurrence. MNT is associated with well-known prognostic factors, such as macroscopic thrombosis (possibly representing regression of macroscopic involvement) and anaplasia. Further prospective studies are needed to clarify the role of MNT as independent prognostic factor.