OBJECTIVE: The aim of this study was to investigate pre-90Y lung shunt fraction (LSF) as a prognostic factor for overall survival (OS) in 90Y (resin/glass) planning 99mTc-MAA hepatopulmonary shunt studies for primary (hepatocellular carcinoma [HCC], intrahepatic cholangiocarcinoma) and metastatic liver tumors. METHODS: A total of 366 consecutive patients with primary and metastatic liver tumors underwent pre-90Y shunt study and 90Y radioembolization (mean age, 59.2 years; 55% were male). MAA (mean activity, 3.65 mCi) was administered via the proper hepatic artery. Shunted lung activity was obtained by planar scintigraphy. Median LSF values for primary tumors and metastases were compared with OS from first 90Y therapy via Kaplan-Meier estimation and log-rank test. Correlations between LSF and tumor involvement on baseline cross-sectional imaging were analyzed using Pearson coefficient (r). Patients with LSF of greater than 20% were deemed unsuitable for 90Y. RESULTS: The study included 79 (21.5%) colorectal, 73 (20%) neuroendocrine, 70 (19.1%) HCC, 40 (10.9%) intrahepatic cholangiocarcinoma, 40 (10.9%) melanoma, 20 (5.5%) breast, and 44 (12%) other tumors including lung and pancreatic cancers. Lung shunt fractions of less than 10% and 10% to 20% were observed in 235 patients (64.2%) and 131 patients (35.8%), respectively. Median LSFs were as follows: colorectal cancer (7.60%), neuroendocrine tumor (7.01%), HCC (11.47%), cholangiocarcinoma (7.00%), melanoma (6.00%), breast cancer (7.00%), and others, including lung and pancreatic metastases to the liver (8.36%). The HCC median LSF was significantly higher than that in non-HCC tumors, 11.47% versus 7.10% (P < 0.001). High LSF (≥ 10%) in HCC correlated with poorer survival from first 90Y compared with low LSF (<10%; 4.5 vs 16.4 months, P = 0.003). Similarly, for metastatic disease, high LSF demonstrated significantly poorer survival compared with low LSF in colorectal liver metastases (13.5 vs 7.0 months, P = 0.013), neuroendocrine liver metastases (33.0 vs 9.1 months, P < 0.001), and melanoma liver metastases (12.0 vs 5.0 months, P = 0.03). No correlation between tumor burden on cross-sectional imaging and LSF was observed (r = 0.35). CONCLUSIONS: In patients who are candidates for 90Y therapy, higher LSF is a poor prognostic factor for OS in HCC and metastatic liver tumors.