Outcomes of patients with stage I testicular cancer following orchidectomy with borderline retroperitoneal lymph node enlargement at diagnosis.

633 Background: Approximately 60% of men diagnosed with testicular cancer present with Stage I disease. Most metastases occur in the retroperitoneal lymph nodes (RPLN); RPLN measuring 8-10 mm in the long axis in the appropriate landing zone are considered highly suspicious, and those measuring > 10 mm usually receive additional surgery, chemotherapy or radiation. Many of these patients’ (pt) RPLN will spontaneously regress without additional treatment. Our goal is to better understand the incidence, natural history, and predictors of such spontaneous RP nodal regressions. Methods: We performed a retrospective chart review of clinical records and staging CT imaging reports from all pts followed at Princess Margaret Cancer Centre (PM) from 2004 – 2024 with Stage I-IIA testicular cancer following orchidectomy. Our primary outcome of interest was the 5-year relapse-free survival (RFS, calculated using the Kaplan–Meier method) of pts with testicular cancer with borderline RPLN (longest dimension 8-14 mm based on first CT scan done within 60 days of orchidectomy) in the appropriate landing zone with no other sites of metastases, and declining or normal tumor markers (AFP, HCG and/or LDH) post-orchiectomy who were initially managed with active surveillance according to a pre-determined schedule with additional interim assessments as deemed appropriate by the treating team. Secondary outcomes included identifying histopathologic predictors of relapse in pts who ultimately went on to require further treatment using a Cox proportional-hazards model. Results: Of the 1535 pts with Stage I-IIA disease, 126 had borderline enlarged RPLN (8.2%). 63.7% were pure seminoma (SEM) and 36.3% were non-seminoma germ cell tumors (NSGCT). Incidence of right, left, and bilateral primaries was 47.6%, 50.8% and 1.6% respectively. Median age at consultation was 33 (SEM; range 19-59) vs 27 (NSGCT; range 19-49) years. Median follow-up was 61.9 (5.8 – 203) months. 5-year RFS was 56% (95% CI 46%-64%) in the entire cohort, 61% (95% CI 49%-71%) in SEM and 48.9% (95% CI 33.7%-62.4%) for NSGCT (p = 0.024 SEM vs NSGCT). Median time to relapse (TTR) was 15.8 (95% CI 6.5-25.0) weeks. 5-year OS was 100% regardless of relapse status. Pure embryonal carcinoma (EC) histology (p = 0.014) and LVI (p = 0.03) were associated with subsequent relapse. Rete testes invasion, primary tumor size, largest LN diameter and number of suspicious nodes were not associated with relapse (p > 0.05 for all). Conclusions: It is reasonable to consider careful close interval follow-up and active surveillance in pts with borderline RPLN and falling or negative tumor markers. Short interval follow-up CT scan (6-8 weeks) after orchidectomy to re-evaluate borderline RPLN may spare overtreatment of men who have been cured with orchiectomy alone. EC histology and LVI were independent predictors of relapse.