Objective: To evaluate the value of yttrium-90 (⁹⁰Y) microspheres in the management of unresectable liver metastases secondary to neuroendocrine tumors (NETs).

Materials and methods: PubMed, EMBASE, the Cochrane Database of Systematic Reviews, and the "gray" literature (Google Scholar) were searched for all studies related to ⁹⁰Y therapy for unresectable liver metastases of NETs.

Results: A total of 11 studies and 7 abstracts involving 870 patients were included in the final analysis. In 11 of these studies, 19.8% (77/388) of patients had undergone transarterial bland embolization (TABE) or transarterial chemoembolization (TACE) before ⁹⁰Y therapy. The median disease control rate among all patients was 86% at 3 months after ⁹⁰Y therapy. The median survival was 28 months, with 1-, 2-, and 3-year survival rates of 72.5%, 57%, and 45%, respectively. The median survival values for patients who received resin- and glass-based ⁹⁰Y treatment were 27.6 and 31.7 months, respectively. The survival values for patients with carcinoid, pancreatic, and unclassified origin of NETs were 56, 31, and 28 months, respectively; the survival values for patients with grade I, II, and III NETs were 71, 56, and 28 months, respectively. Carcinoid syndrome was reported in 52.4% (55/105) of patients, and 69.1% of those with clinical symptoms demonstrated improvement in symptoms after ⁹⁰Y radioembolization. Complications were reported in 9 studies, including radiation gastritis (n = 4), duodenal ulcer (n = 2), death due to liver failure (n = 1), and radiation cholecystitis (n = 1). The most common side effects were abdominal pain (median, 32.6%), nausea/vomiting (median, 32.5%), and fatigue (median, 30.4%).

Conclusions: ⁹⁰Y radioembolization can be used as an alternative therapy for unresectable liver metastases of NETs, with an improved survival rate and tumor response. This treatment is also effective for patients who have undergone unsuccessful TABE/TACE therapy and for the relief of symptoms in patients with carcinoid syndrome.