The trial investigates a stage-adapted (stage IIA or IIB) de-escalation of the standard treatments in the context of a multimodality treatment with chemo- and radiotherapy in seminoma patients. The goal is to safely de-escalate treatment while maintaining/enhancing efficacy, which is not a standard practice yet.

Therapy de-escalation in stage IIA/B seminoma represents an unmet need in clinical practice; efficacy of modern standard of care therapies for these patients is high and only a few patients show disease recurrence but short- and long-term toxicities are a major concern. The magnitude of long-term toxicities is often associated with the intensity of the prescribed treatment modality. A higher cumulative dose of chemotherapy agents and radiation dose has been linked to a sharp increase in long-term sequelae. Combining treatment modalities and diversifying toxicity may thus provide an opportunity to limit long-term treatment sequelae.

In this trial carboplatin, cisplatin and etoposide are the Investigational Medicine Products (IMPs). They are all medications with a marketing authorization for several solid tumor types and are standard practice in the treatment of testicular cancer in Switzerland and in the European Union (EU).

Radiotherapy is also a standard therapy in this indication.

However, the trial investigates a stage-adapted (stage IIA or IIB) de-escalation of these standard treatments in the context of a multimodality treatment with chemo- and radiotherapy. The goal is to safely de-escalate treatment while maintaining/enhancing efficacy, which is not a standard practice yet.

The SAKK 01/18 trial is designed with the aim to answer these three questions:

• Can the dose of involved-node radiotherapy be safely reduced in the context of multimodality treatment with chemo- and radiotherapy?
• Can a more potent chemotherapy in the form of cisplatin/etoposide reduce the rate of distant failure in comparison to carboplatin?
• Can a combination of cisplatin/etoposide and involved-node radiotherapy pose a potent treatment regime for patients with recurrence after adjuvant carboplatin or radiotherapy for stage I seminoma? Furthermore, as active surveillance is becoming standard of care in stage I seminoma, it is projected that the amount of patients in need of treatment with stage IIA/B disease will rise, due to more patients developing disease progression during active surveillance.

The trial design, trial treatment and trial specifics are a consensus among the Swiss Urogenital Tumors Project Group and the Swiss Radio-oncology Section from the Swiss Group for Clinical Cancer Research (SAKK) and the German Testicular Cancer Study Group (GTCSG).

Inclusion Criteria:

• Written informed consent according to ICH/GCP (International Council on Harmonization/Good Clinical Practice) regulations before registration and prior to any trial specific procedures
• Histologically confirmed classical seminoma treated with primary inguinal orchidectomy or partial orchidectomy
• Patients with a seminoma stage IIA or IIB, either newly diagnosed or recurrent after primary active surveillance, adjuvant carboplatin or radiotherapy for stage I disease. The tumor stage is pT1-4 cN1-2 cM0 according to UICC TNM 8th edition 2016. Patients with a recurrent seminoma stage IIA or IIB are only eligible in case of progression under active surveillance or recurrence after adjuvant carboplatin or radiotherapy for stage I disease
• Stage IIA, in patients with equivocal lymph node enlargement, needs to be confirmed with a repeated CT/MRI scan of the abdomen (suggested timeframe: 4 weeks after the previous scan) in order to rule out false positive lymph node enlargement.

Patients with a prior malignancy treated with curative intention are eligible if all treatment of that malignancy was completed at least 5 years before registration and the patient has no evidence of disease at registration. Less than 5 years is acceptable for malignancies with low risk of recurrence and/or no late recurrence. Patients with a germ cell neoplasia in situ (GCNIS) or contralateral localized treated seminoma are eligible

• Diagnostic CT or MRI or FDG-PET-CT of the chest, abdomen and pelvis within 28 days prior to registration, showing stage IIA/B disease. I.v. contrast medium has to be administered
• Age ≥ 18 years
• WHO performance status 0-2
• Baseline PRO questionnaires have been completed
• Adequate bone marrow function: neutrophil count ≥ 1.0 x 109/L, platelet count ≥ 100x 109/L
• Adequate renal function: creatinine clearance ≥ 60 ml/min calculated according to the CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) formula
• Patient agrees to use highly effective contraception and not to donate sperm or to father a child during trial treatment and during 12 months thereafter. Patient has been proposed sperm conservation.

Exclusion criteria

• Any other histological component than seminoma
• Elevated levels of Alpha-1-Fetoprotein AFP (≥ 2x ULN)
• Involved nodes (metastatic) in previously irradiated localizations in the abdomen or pelvis
• Any anti-cancer therapy after primary tumor resection in patients presenting with primary stage IIA/B seminoma
• Any serious underlying medical condition (i.e. current renal insufficiency, severe hepatic insufficiency, severe bone marrow dysfunction, tumor bleeding, major hearing defects) or serious co-morbidity which could impair the ability of the patient to participate in the trial (according to investigator's judgment)
• Any treatment in a clinical trial within 28 days prior to registration
• Any concomitant drugs contraindicated for use with the trial drugs according to the approved product information or contraindicated for use with radiotherapy
• Known hypersensitivity to trial drugs or to any component of the trial drugs
• Any other serious underlying medical, psychiatric, psychological, familial or geographical condition, which in the judgment of the investigator may interfere with the planned staging, treatment and follow-up, affect patient compliance or place the patient at high risk from treatment-related complications.

Additional German specific exclusion criteria - not to be considered for Swiss patients

• Patient who is dependent on the sponsor or the investigators according to ICH/GCP E6(R2), guideline
• Patient who has been committed to an institution by virtue of an order issued either by the judicial or the administrative authorities according to § 40a (2) AMG.