OBJECTIVES: Searching for testicular intraepithelial neoplasia (TIN; carcinoma in situ) in the contralateral testis of patients with germ cell tumour (GCT) may early disclose contralateral GCT. A single biopsy of the testis is thought to accurately detect TIN. Reports on false-negative biopsies have challenged this view. We investigated whether systematic two-site biopsies are more sensitive than single biopsies. We also studied the prevalence of contralateral TIN in a large patient sample. METHODS: A total of 2318 patients with testicular GCT underwent contralateral double biopsy. All of the biopsy pairs were examined histologically for spermatogenesis and for presence of TIN. Statistical analysis involved first, overall prevalence of contralateral TIN; second, associations of clinical factors with TIN; third, frequency of discordant findings regarding TIN among biopsy pairs; and finally, associations of discordance with clinical factors. RESULTS: A total of 119 patients (5.13%; 95% confidence interval [CI], 4.27-6.11) had contralateral TIN. TIN is associated with poor spermatogenesis (relative risk [RR] 15.74; 95%CI, 10.38-23.86) and with testicular atrophy (RR 3.78). According to TIN, 31.1% of biopsy pairs were discordant. Discordance was significantly less frequent in atrophic testes and in patients with poor spermatogenesis. CONCLUSIONS: We confirmed the prevalence of contralateral TIN to be about 5%. TIN is significantly associated with poor spermatogenesis and with testicular atrophy. The diagnostic extra yield imparted by double biopsies is 18%. Discordant results regarding TIN are predominantly encountered in normal-sized testicles. The new standard in diagnosing TIN is two-site biopsy.
