Long-Term Follow-Up Confirms Benefits of Low-Dose Seminoma Treatment

Long-term follow-up of the international, multicenter phase 2 trial SAKK 01/10 found that single-dose carboplatin and involved-node radiotherapy (INRT) yielded an exceptional long-term performance with a highly favorable safety profile in stage IIa/b seminoma.¹

The 10-year overall progression-free survival (PFS) was 92.8% (95% CI, 86.1%-96.3%), 10-year overall survival was 99.1% (95% CI, 93.6%-99.9%) and seminoma-specific survival was 100%. Crucially, no late recurrences were observed since the primary analysis. In stage IIa seminoma, the 10-year PFS was 95.2% (95% CI, 82.2%-98.8%), and in stage IIb it was 91.3% (95% CI, 81.6%-96.0%).

Toxicity and Safety Profile

The treatment regimen was exceptionally well tolerated, with minimal toxicity observed in both the acute and long-term phases. Over 50% of patients experienced no acute adverse events (AEs). For those who did, events were predominantly low-grade and manageable. A total of 2% of patients experienced grade 3 thrombocytopenia, 1% experienced grade 4 thrombocytopenia, 4% grade 3 neutropenia, and 1% grade 3 vomiting.

The extended follow-up specifically addressed concerns about late toxicities, which were found to be minimal. Only 1 late AE was identified as possibly related to the treatment: a non–ST-elevation myocardial infarction that occurred in a 53-year-old patient 7 years after treatment.

Eight patients developed second primary tumors. Critically, all of these tumors occurred outside the radiotherapy fields and were not deemed to be related to the trial treatment.

Trial Overview and Design

The SAKK 01/10 study was a single-arm, phase 2 therapy optimization trial designed to evaluate a combined modality treatment for seminoma. The objective was to assess the efficacy and safety of single-dose carboplatin followed by involved-node radiotherapy for stage IIa/b seminoma.

The trial ran from 2012 to 2018 across 20 centers in Switzerland and Germany. A total of 116 patients were enrolled with a median age of 40 years (range, 22–68). Forty-six patients had stage IIa disease, and 70 patients had stage IIb disease. The median lymph node size was 2.5 cm (IQR, 1.5–3.3).

The treatment regimen consisted of 2 components administered over a 3-week period:

1. Chemotherapy: A single dose of carboplatin at AUC7
2. Radiotherapy: INRT with doses adjusted by stage:
   1. Stage IIa: 30 Gy
   2. Stage IIb: 36 Gy
      1. This approach resulted in a 75% median reduction of the irradiated volume compared with traditional methods.

The initial results, presented at the European Society for Medical Oncology (ESMO) Congress 2021 and published in The Lancet, already indicated strong efficacy. With a median follow-up of 4.5 years, the 3-year PFS was 93.7% (90% CI, 88.5%-96.6%) overall, 92.5% in stage IIa disease, and 92.6% in stage IIb disease.²

Conclusions and Future Directions

Based on the comprehensive evidence, the study investigators, led by Alexandros Papchristofilou, MD, University of Basel, noted, "Single-dose carboplatin and involved-node radiotherapy for seminoma stage IIA/B should be considered a new standard of care, given its efficacy, minimal acute toxicity, and long-term safety."¹

Research in this area is ongoing with the follow-on trial, SAKK 01/18 (NCT03937843). The first results from this subsequent study are anticipated in 2026.

REFERENCES

1. Papachristofilou A, et al. Single-dose carboplatin and involved-node radiotherapy for seminoma stage IIA/B: long-term follow-up from the international multicenter phase II trial SAKK 01/10. Presented at: ESMO Congress 2025; October 17-21, 2025; Berlin, Germany. Abstract 1038MO.

2. Papchristofilou A, Bedke J, Hayoz S, et al. Single-dose carboplatin followed by involved-node radiotherapy for stage IIA and stage IIB seminoma (SAKK 01/10): a single-arm, multicentre, phase 2 trial. Lancet Oncol. 2022;23(11):1441-1450. doi:10.1016/S1470-2045(22)00564-2