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Background: This report examines (99m)Tc-etarfolatide imaging to identify the presence of folate receptor (FR) on tumors of women with recurrent/refractory ovarian or endometrial cancer and correlates expression with response to FR-targeted therapy (vintafolide)., Patients and Methods: In this phase II, single-arm, multicenter study, patients with advanced ovarian cancer were imaged with (99m)Tc-etarfolatide before vintafolide treatment. Up to 10 target lesions (TLs) were selected based on Response Evaluation Criteria In Solid Tumors criteria using computed tomography scans. Single-photon emission computed tomography images of TLs were assessed for (99m)Tc-etarfolatide uptake as either FR positive or negative. Patients were categorized by percentage of TLs positive and grouped as FR(100%), FR(10%-90%), and FR(0%). Lesion and patient response were correlated with etarfolatide uptake., Results: Forty-nine patients were enrolled; 43 were available for analysis. One hundred thirty-nine lesions were (99m)Tc-etarfolatide evaluable: 110 FR positive and 29 FR negative. Lesion disease control rate (DCR = stable or response) was observed in 56.4% of FR-positive lesions versus 20.7% of FR-negative lesions (P < 0.001). Patient DCR was 57%, 36%, and 33% in FR(100%), FR(10%-90%), and FR(0%) patients, respectively. Median overall survival was 14.6, 9.6, and 3.0 months in FR(100%), FR(10%-90%), and FR(0%) patients, respectively., Conclusions: Overall response to FR-targeted therapy and DCR correlate with FR positivity demonstrated by (99m)Tc-etarfolatide imaging., Clinical Trial Number: NCT00507741.