This phase II clinical trial evaluates the efficacy, safety and tolerability of Atezolizumab in addition to standard of care chemotherapy (Platinum/Etoposide) in LCNEC.

Inclusion Criteria:

1. Written informed consent

2. Patients with locally advanced or metastatic large-cell neuroendocrine carcinoma of the lung (LCNEC) without curative treatment options (patients with mixed histology are eligible if LCNEC is the predominant histology i.e. ≥50%)

3. Previously untreated with systemic therapy (note: patients relapsing after curative radio chemotherapy or adjuvant chemotherapy are eligible if relapse occurs ≥6 months after discontinuation of curative treatment)

4. Planned treatment with Carboplatin or Cisplatin and Etoposide (SoC)

5. ECOG performance status: 0-2

6. age ≥18 years

7. measurable disease according to RECIST v1.1

8. adequate organ function defined as:

   1. ALAT/ASAT ≤2.5x ULN or ≤3.5x ULN in case of liver metastases
   2. Bilirubin ≤1.5x ULN or ≤2.5x ULN in case of liver metastases
   3. Creatinine ≤1.5x ULN or Creatinine clearance according to Cockroft-Gault >60 ml/min
   4. Neutrophils ≥1 Gpt/l, Platelets >50 Gpt/l unless caused by bone marrow carcinosis

Exclusion Criteria:

1. Symptomatic brain metastases (patients with asymptomatic brain metastases are allowed provided they are stable without steroid treatment for at least 3 weeks)
2. Severe autoimmune disease (patients with endocrine autoimmune disorders are allowed as long as they are on stable substitution treatment)
3. Severe uncontrolled infection
4. Prior treatment with either Atezolizumab or other immune checkpoint inhibitor
5. Any prior treatment for metastatic disease