The aim of this prospective, randomized, controlled clinical trial is to evaluate the efficacy and safety of iparomlimab and tuvonralimab injection (QL1706) plus lenvatinib and etoposide-based platinum chemotherapy, consisting of etoposide plus cisplatin or carboplatin, compared with etoposide-based platinum chemotherapy alone as first-line treatment for patients with extrapulmonary neuroendocrine carcinoma. Potential predictive biomarkers will also be explored through analyses of tumor tissue, peripheral blood, and relevant clinical and pathological data.