1008 - Delays In Adjuvant Therapy Initiation for Wilms Tumor: Institutional Patterns and Clinical Impact on Disease Control

Purpose/Objective(s): Current guidelines recommend that adjuvant radiotherapy (RT) and chemotherapy (CT) start within 14 days after surgery for local stage III favorable histology or anaplastic Wilms tumor (WT), with few specified exceptions. Achieving this time frame in the context of logistical and medical considerations can be difficult.

Materials/Methods: To assess patterns and outcomes of adjuvant therapy delays, we retrospectively reviewed patients with local stage III favorable histology or local stage I-III anaplastic WT treated at a single institution between 2013 and 2022 on an institutional review board-approved protocol. Patients who received RT elsewhere, who did not have RT tumor bed coverage (at least one side for stage V cases), or who had prior history of WT were excluded. Adverse biology included 1q gain, loss of heterozygosity (LOH) of both 1p and 16q, or LOH of either 1p or 16q plus lymph node positivity. Multivariable logistic regression models were used to calculate adjusted odds ratios (aOR), which are reported with 95% confidence intervals (CI).

Results: Of the 79 patients identified, 62% were female, 44% were white, and median age was 3 years (range: 8 months – 11 years). Tumors were anaplastic histology in 9%, bilateral in 8%, and adverse biology in 32%. Neoadjuvant CT was used for 40% of patients, of whom 26% had blastemal predominant histology at delayed nephrectomy. Adjuvant RT was directed to the flank in 82% and whole abdomen in 18%, with 92% receiving three-dimensional plans, 6% intensity-modulated RT, and 1% proton therapy. Median start of RT after surgery was 19 days (range: 7 – 146), with 65% classified as delayed (>14 days after surgery). RT delay was due to medical complications for 10%, lung metastasis response assessments for 12%, and care coordination for 78%. Median start of adjuvant CT after surgery was 13 days (range: 5 – 32), with 30% classified as delayed (>14 days after surgery). CT delay was due to medical complications for 26% and care coordination for 74%. Disease recurrence, tumor bed recurrence, and disease-related death occurred in 18%, 9%, and 14% of patients, respectively. RT delay was associated with increased disease recurrence (p = 0.03) and disease-related death (p = 0.03), as shown in the table below.

Conclusion: The high rate of adjuvant therapy delays for WT is concerning, particularly since delayed RT appears to be associated with worse disease outcomes. Since treatment delays are not always avoidable, further research is needed to understand the mechanisms of disease recurrence in this context and identify patient-centered strategies for addressing this risk.