Testicular ultrasonographic features predict future risk for bilateral testicular germ cell tumour: A long-term single centre follow-up study

Background: Bilateral testicular germ cell tumours (B-GCT) are rare, with an incidence of 2-5%, and can be classified as synchronous (sB-GCT) or metachronous (mB-GCT). Our study aimed to identify clinical, biochemical, and radiological risk factors for mB-GCT in a cohort of patients with GCT at a single tertiary referral centre. Methods: This retrospective case-control study included patients with GCT referred to Policlinico Umberto I-Sapienza University of Rome, from 2005 to 2023. We evaluated clinical history, testicular ultrasound features, hormone levels, semen analysis, histological characteristics, staging, and treatments. mB-GCTs were compared with unilateral GCT patients with a follow-up longer than the median time-to-onset of the second tumour. Results: Of 319 patients, 52 experienced B-GCT, with a median time-to-onset of the second tumour of 62 months (range: 8-229). The mB-GCT group showed higher gonadotropin levels (FSH 13.6mUI/mL vs. 7.4mUI/mL, p < 0.001; LH 6.6mUI/mL vs. 3.9mUI/mL, p = 0.004), lower sperm concentration (27 x 106/ejaculate vs. 78 x 106/ejaculate, p = 0.009), smaller residual testis volume (10.4 mL vs. 16.3 mL, p < 0.001), more inhomogeneous echotexture [57.5% vs. 14%, p < 0.001], and presence of microlithiasis (75% vs. 19.5%, p < 0.001). Kaplan-Meier curves confirmed that ultrasound features of the residual testis increased the cumulative risk of developing a second tumour. Microlithiasis was a strong independent predictor (OR 30.712, 95% CI 3.357-280.942, p = 0.002). Conclusions: Histological features of the first tumour or its treatment do not influence the onset of a second tumour. However, low residual testis volume, inhomogeneous echotexture, and microlithiasis significantly increase this risk. A comprehensive evaluation of the residual testis at baseline is essential for developing a personalised surveillance programme in GCT survivors, with regular ultrasound follow-up recommended beyond the conventional 5-year limit.