Despite the fact that the majority of the patients with limited disease SCLC will respond very well to the standard treatment, a great proportion will relapse within 12 - 24 months.

Several studies in patients with lung cancer suggested a possible favourable association between the increased presence of immunologically active cells in the tumour and survival. Nivolumab and ipilimumab are proteins, which help your immune system to attack and destroy cancer cells by your immune cells. Early clinical trials with nivolumab and ipilimumab have shown activity in a broad range of cancers, including SCLC.

The aim of the current study is to investigate the efficacy (how well the treatment works) and tolerability (how severe the side effects are) of the standard treatment (chemotherapy and radiotherapy) alone, compared with the standard treatment followed by nivolumab and ipilimumab in patients with limited SCLC.

At the time of diagnosis, 30% of patients with small cell lung carcinoma (SCLC) will have limited stage disease, now called stage I-IIIB (IASLC). The outcome of limited disease SCLC is still poor, with a median survival of 16 to 24 months with current forms of treatment and only 15-25% long term survivors.

Combining chemotherapy and thoracic radiotherapy is the standard treatment approach in limited-stage SCLC with a combination of platinum compounds (cis- or carboplatin) and etoposide and cisplatin (PE) as the backbone regimen. Concurrent chemo-radiotherapy is superior to sequential treatment and early thoracic irradiation starting with first or second cycle of chemotherapy appears beneficial. Hyperfractionated accelerated radiotherapy has been shown to be more efficacious than radiotherapy given in a long overall treatment time. However, availability and routine-use of hyperfractionated radiotherapy remains a matter of debate. Therefore, in this trial, both radiotherapy schedules of accelerated twice-daily administration or once-daily radiotherapy are accepted. The choice of schedule is a stratification factor for randomisation.

The adaptive immune response is triggered via effector T-cells, antigen-presenting cells (APCs) and co-stimulatory signals mediated by T cell receptors such as CD28. The interplay of these signals results in the activation and clonal proliferation of T cells.

T-cell proliferation is tightly regulated in order to avoid autoimmunity. The balance between co-stimulatory signals mediated by CD28 and co-inhibitory signals via so called immune checkpoint receptors is crucial for the maintenance of self-tolerance and to protect tissues from damage during normal immune response. After activation, T-cells express the immune checkpoint receptors cytotoxic T-lymphocyte antigen-4 (CTLA-4) and programmed cell death protein 1 (PD-1).

CTLA-4- and PD-1 expressing T-cells play a critical role in maintaining self-tolerance but are also responsible for non-responsiveness to tumour antigens. Cancer cells escape from im-mune surveillance by expressing immune checkpoint receptors. The goal of immune check-point inhibitor therapies is not to activate the immune system to attack particular targets on tumour cells, but rather to remove inhibitory pathways that block effective antitumour T cell responses.

Ipilimumab is a monoclonal antibody that binds to CTLA-4 and inhibits the interactions with the ligands B7.1 and B7.2, Nivolumab is a monoclonal antibody that targets PD-1. Engagement of PD-1 by its natural ligands, PD-L1 and PD-L2, results in an inhibition of T cell proliferation, survival and cyto-kine secretion. Nivolumab abrogates this interaction between PD-1 and its ligands.

The two antibodies, nivolumab and ipilimumab, do not only target different immune cell receptors, they also regulate distinct inhibitory pathways and have therefore non-overlapping mechanisms of action. Anti-CTLA-4 therapies seem to drive T-cells into tumours, resulting in an increased number of intratumour T-cells and a concomitant increase in IFN-y. This in turn can induce the expression of PD-L1 in the tumour microenvironment, with subsequent inhibition of antitumour T-cell responses, but may also increase the chance of benefit from anti-PD-1 and anti-PD-L1 therapies. A combination treatment with anti-CTLA-4 (e.g. ipili-mumab) plus anti PD-1 (e.g. nivolumab) or anti-PD-L1 antibodies should enable the creation of an immunogenic tumour microenvironment with subsequent clinical benefit for patients.

Nivolumab monotherapy has been approved for the treatment of advanced melanoma (FDA, EMA, and Japan) and previously treated squamous NSCLC (FDA, positive CHMP opin-ion). Nivolumab and ipilimumab improved PFS compared to nivolumab or ipilimumab alone in a study in melanoma (CA209067).

In a randomised open-label phase I/II trial (CheckMate 032), evaluating nivolumab with or without ipilimumab in pretreated SCLC patients with progressive disease and sensitive or refractory to platinum based chemotherapy, based on an interim analysis a response rate of 33% and disease stabilisation in 22% was observed for the combination of nivolumab and ipilimumab compared to 18% response rate and 20% stable disease with nivolumab mono-therapy.

Both, nivolumab monotherapy and nivolumab plus ipilimumab combination treatment were tolerable for the treatment of SCLC, and no new safety profile was identified compared to the profile of nivolumab with or without ipilimumab in other anti-cancer therapies.

Nivolumab plus ipilimumab will be administered as a consolidation treatment after comple-tion of a standard treatment including chemo-radiotherapy and prophylactic cranial irradia-tion (PCI).

Inclusion Criteria for enrolment:

• Histologically or cytologically confirmed small cell lung carcinoma.
• Untreated limited-stage disease (with the exception of one cycle of chemotherapy given prior to enrolment) as defined by stage I-IIIB based on 7th TNM classification (IASLC classification for SCLC proposal). M0 proven by whole body FDG-PET CT including a contrast-enhanced CT of thorax and upper abdomen (incl. liver, kidney, adrenals); OR contrast-enhanced CT of thorax and upper abdomen (incl. liver, kidney, adrenals) and bone scan; AND brain MRI (or contrast enhanced CT of the brain) within 28 days before start of chemotherapy.
• Age ≥ 18 years.
• ECOG performance status 0-1.
• Adequate haematological function: haemoglobin > 9 g/dL, neutrophils count >1.5×109/L, platelet count > 100 × 109/L.
• Adequate liver function: total bilirubin < 2.5 × ULN, ALT and/or AST < 2.5 × ULN, alkaline phosphatase < 5 ULN.
• Adequate renal function: Calculated creatinine clearance ≥ 30 mL/min (Cockroft-Gault).
• Pulmonary function FEV1 of 1.0L or > 40% predicted value and DLCO > 40% predicted value.
• Patient capable of proper therapeutic compliance, and accessible for correct follow-up.
• Women of childbearing potential, including women who had their last menstrual period in the last 2 years, must have a negative serum or urine pregnancy test within 7 days before beginning of chemotherapy.
• All sexually active men and women of childbearing potential must use an effective contraceptive method (two barrier methods or a barrier method plus a hormonal method) during the study treatment and for a period of at least 12 months following the last administration of trial drugs.
• Measurable or evaluable disease (according to RECIST 1.1 criteria). Not eligible: patients with only one measurable or evaluable tumour lesion which was resected or irradiated prior to enrolment.
• Written Informed Consent (IC) must be signed and dated by the patient and the investigator prior to any trial-related intervention for a) Chemo-radiotherapy treatment and PCI, and subsequent randomisation, including mandatory biological samples b) Optional biological material collection, long-term storage and future use of biological material for translational research.

Exclusion Criteria for enrolment:

• Patient with mixed small-cell and non-small-cell histologic features.
• Patient with pleural or pericardial effusions proven to be malignant.
• Patients who have had in the past 5 years any previous or concomitant malignancy EXCEPT adequately treated basal or squamous cell carcinoma of the skin, in situ carcinoma of the cervix or bladder, in situ ductal carcinoma of the breast (if no RT was involved).
• Patients with other serious diseases or clinical conditions, including but not limited to uncontrolled active infection and any other serious underlying medical processes that could affect the patient's capacity to participate in the study.
• Ongoing clinically serious infections requiring systemic antibiotic or antiviral, antimicrobial, antifungal therapy.
• Known or suspected hypersensitivity to nivolumab or ipilimumab or any of their excipients.
• Substance abuse, medical, psychological or social conditions that may interfere with the patient's participation in the study or evaluation of the study results.
• Documented history of severe autoimmune or immune mediated symptomatic disease that required prolonged (more than 2 months) systemic immunosuppressive (e.g. steroids) treatment, such as but not limited to ulcerative colitis and Crohn´s disease, rheumatoid arthritis, systemic progressive sclerosis (scleroderma), systemic lupus erythematosus, or autoimmune vasculitis (eg, Wegener's granulomatosis).
• Subjects with an autoimmune paraneoplastic syndrome requiring concurrent immunosuppressive treatment.
• Interstitial lung disease or pulmonary fibrosis.
• Women who are pregnant or in the period of lactation.
• Sexually active men and women of childbearing potential who are not willing to use an effective contraceptive method during the study.
• Patients with any concurrent anticancer systemic therapy (except for chemotherapy cycle 1).
• HIV, active Hepatitis B or Hepatitis C infection.
• Previous radiotherapy to the thorax (prior to inclusion), including RT for breast cancer.
• Planned radiotherapy to lung of mean dose > 20 Gy or V20 > 35 %.
• Patients who received treatment with an investigational drug agent during the 3 weeks before enrolment in the study.
• Prior chemotherapy or radiotherapy for SCLC. Exception: one cycle of chemotherapy (as specified to section 10.2 of the protocol) may be administered prior to enrolment.

Inclusion Criteria for randomisation:

• Chemo-radiotherapy completed per protocol: 4 cycles of chemotherapy, ≥85% of PTV of thoracic radiotherapy, as well as completed, mandatory PCI.
• Non-PD after chemo-radiotherapy and PCI.
• ECOG performance status 0-2.
• Recovery of all adverse events to a grade ≤1, except for fatigue, appetite, oesophagitis and renal impairment (where ≤2 is allowed) and alopecia (any grade).
• Women of childbearing potential, including women who had their last menstrual period in the last 2 years, must have a negative serum or urine pregnancy test within 7 days before randomisation.

Exclusion criteria for randomisation:

• Less than 4 cycles of chemotherapy administered, less than 85% PTV of thoracic radiotherapy delivered, or PCI not completed.
• Progressive disease after chemo-radiotherapy and PCI.