This study is for patients with neuroendocrine carcinoma (NEC) originating outside of the lung. This study is being done to see if the combination of atezolizumab, an immunotherapy drug, with a platinum drug (cisplatin or carboplatin) and etoposide better or worse than a platinum drug and etoposide for patients with advance or metastatic neuroendocrine carcinoma originating outside the lung