This study will enroll patients with central lab confirmed NCAM (CD56 IHC) positive metastatic neuroendocrine neoplasms that have progressed after standard of care treatment. CTX-471 to be administered as an intravenous (IV) infusion at either 0.3 mg/kg or 0.6 mg/kg every 2 weeks until disease progression or unacceptable toxicity. The study will be conducted in two stages. In Stage 1, 18 patients will be accrued for each dose level. If there are less than 2 objective responses in these 18 patients at either dose level, the dose level will be stopped. Otherwise, an additional 22 patients will be accrued in Stage 2 with 11 patients for each dose level.