BACKGROUND: Increasing concerns about late effects after adjuvant treatment for stage I seminoma have made surveillance an attractive alternative.

OBJECTIVE: To evaluate the surveillance strategy in a nationwide cohort study.

DESIGN, SETTING, AND PARTICIPANTS: A retrospective, population-based study of Danish patients diagnosed with stage I seminoma between 1984 and 2008 and followed for 5 yr (n=1954). Patient data were linked with national registries on November 30, 2012, to obtain information on late relapse, vital status, and cause of death.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS: Disease-specific survival (DSS), overall survival, relapse rates, time to relapse, detection of relapse, and prognostic factors for relapse were described for the cohort. The Kaplan-Meier method was used to determine survival probabilities. A Cox proportional hazards model was used for multivariate analysis of prognostic factors.

RESULTS AND LIMITATIONS: Median follow-up time was 15.1 yr. In total, 369 patients relapsed after a median 13.7 mo. DSS after 15 yr was 99.3%. Tumor size was a significant factor for relapse. Either vascular invasion or invasion of epididymis was significant if the other factor was excluded from analysis. Limitations include the retrospective nature of the study and the number of missing values in analysis.

CONCLUSIONS: In the world's largest study of stage I seminoma patients, we found surveillance to be a safe alternative to adjuvant therapies. Tumor size was a significant factor for relapse, together with either invasion of epididymis or vascular invasion.

PATIENT SUMMARY: In this nationwide study, we looked at the outcomes of patients with stage I seminoma followed for 5 yr. We found that surveillance is a safe alternative to adjuvant treatment.