Supplementary Material for: Incidence and clinical features of inguinal metastases of testicular germ cell tumors

Introduction
Half of all patients with testicular germ cell tumours (GCTs) present with metastases to retroperitoneal lymph nodes or visceral organs. Inguinal metastases (I/M) are very rare. We aimed to evaluate the relative frequency and clinical features of I/M and to look for predisposing factors.
Methods
A cohort of 740 GCT patients treated between 2010-2022 was analyzed. The frequency of I/M and their clinical features were statistically compared among the subgroups.
Results
Eight patients had I/M, with a median age of 55 years, all of whom had primary seminoma, six had previous groin surgery. The relative frequency of I/M is 1.1% and 8.3% in the GCT patient cohort and the metastasized seminoma subgroup, respectively. All patients were cured, six underwent surgery and additional chemotherapy, and two received cisplatin-based chemotherapy alone.
Discussion
Inguinal metastases occur in approximately 1% of GCT patients. Prior groin surgery, bulky retroperitoneal metastases and possibly histology of seminoma represent risk factors for I/M. The presence of I/M does not adversely affect prognosis, and all cases can be cured with standard therapeutic measures. Lymph node excision may be required to establish the diagnosis. In patients with risk factors, follow-up examinations should include the groins.