Background: SWOG/CCTG S1823/GCC-001 is a non-interventional translational prospective cohort investigation with a primary endpoint of defining pre-treatment operational characteristics of the liquid germ cell cancer biomarker microRNA 371a-3p in predicting the presence of active germ cell malignancy. Opened in June 2020, 813 of the projected 956 patients have been registered with anticipated completion of accrual in early 2024. While analysis of the final endpoint awaits complete accrual and sufficient follow-up, S1823 creates a rich template of baseline clinical information and real-world treatment. Herein, we report baseline patterns of care in modern day real-world care delivery for Clinical Stage I (CSI) germ cell tumors across academic and community practices in North America. Methods: Data is obtained from case report forms and source documents for 547 S1823 enrollees with CSI seminoma or nonseminoma. Aggregate baseline clinical data unrelated to the primary endpoint are described to understand baseline clinical characteristics and management recommendations for CSI germ cell tumors. Results: Clinical characteristics and management recommendations for CSI are described in the table. The leading contributor to date is the Kaiser Permanente NCI NCORP followed by Canadian Institutions which together make up 38% of accruals from top level institutions. The majority of these largely young males were overweight or obese (67%). S1823 did not stipulate management which was at the discretion of local institutions/investigators. Active surveillance is the dominant strategy in both CSI seminoma and nonseminoma (85% overall). In CSI seminoma, adjuvant treatment with radiation is very rare (1/547) and adjuvant treatment with single agent carboplatin (1 or 2 cycles) is uncommon (4%). In CSI nonseminoma, adjuvant retroperitoneal lymph node dissection is also uncommon (3%) as is adjuvant chemotherapy with BEP X 1 or 2 (6%). Conclusions: In this large prospective multi-institutional observational cohort, surveillance appears to be the predominant management strategy for CSI germ cell tumors with very limited use of adjuvant chemotherapy or RPLND and virtual elimination of recommendation for radiation therapy for seminoma. Clinical trial information: NCT04435756.

Sem= seminoma; Non-sem= nonseminoma; BMI= body mass index; BEP= Bleomycin, Etoposide, Cisplatin; Carbo= Carboplatin.