This is a single-arm, multicenter phase Ⅱ study to evaluate the therapeutic efficacy and safety of chidamide + sintilimab + bevacizumab in subjects with advanced extrapulmonary neuroendocrine carcinoma who have failed first-line standard therapy. The primary purpose is to assess the objective response rate (ORR) of chidamide + sintilimab + bevacizumab in the above-mentioned subjects, with a planned enrollment of 34 subjects with advanced extrapulmonary neuroendocrine carcinoma who have failed first-line standard therapy.