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MP49-14 PRIMARY TUMOR SIZE THRESHOLDS IN STAGE IA TESTICULAR SEMINOMA: IMPLICATIONS FOR ADJUVANT THERAPY AFTER ORCHIECTOMY AND SURVIVAL

INTRODUCTION AND OBJECTIVES: Primary tumor size (PTS) is the main prognostic factor for relapse in clinical stage (CS) IA testicular seminoma and the Tumor-Node-Metastasis (TNM) staging system now subcategorizes pT1 tumors into pT1a (<3 cm) and pT1b (≥3 cm). We attempted to assess PTS as a prognosticator for overall survival (OS) and to evaluate the comparative effectiveness of active surveillance (AS) versus adjuvant therapy (AT) in patients with large primary tumors (LPT). METHODS: In the National Cancer Database (2004-2014), 2455 (47.7%) and 2685 (52.3%) patients with CS IA seminoma were treated with AS and AT, respectively. A cut-point analysis was performed to determine the optimum PTS threshold predicting OS at 5 years after orchiectomy. Inverse-probability of treatment weighting (IPTW)-adjusted Kaplan-Meier curves and Cox regression analyses were used to compare OS of patients with LPT treated with AS versus AT. RESULTS: Pathologic T-stage did not predict OS and no OS benefit was noted in pT1b patients treated with AT. The optimum PTS cut-point was 5-cm. In multivariable analysis, patients with LPT had an increased risk of overall mortality (HR=1.87, P=0.003). Kaplan-Meier curves revealed that OS was superior in patients with LPT treated with AT (IPTW-adjusted log-rank P=0.029). In IPTW-adjusted Cox regression analysis, AT was associated with an OS benefit in patients with LPT (HR=0.59, P=0.017). CONCLUSIONS: PTS was an independent predictor of OS in CS IA seminoma. An OS benefit was noted for individuals with LPT managed with AT versus AS. These findings may warrant refinement of the TNM staging system and clinical practices. Figure. No caption available. Source of Funding: None