6049 Background: The clinical utility of PET/CT in patients with suspected cancer recurrence remains unclear. The aim of this multi-center, prospective, comparative effectiveness study is to assess the impact of PET/CT on clinical management of patients with suspected cancer recurrence. Methods: Patients were eligible if cancer recurrence (non-small cell lung, breast, head and neck, ovarian, esophageal, Hodgkin’s or non-Hodgkin’s lymphoma) was clinically suspected, and if conventional imaging (e.g. X-ray, ultrasound, CT, or MRI) was non-diagnostic. As a pre-requisite to PET/CT booking, clinicians were asked at enrolment to indicate their planned management if PET/CT were not available. Patients then underwent ¹⁸FDG-PET/CT. Clinicians were then asked to indicate their management plan based on PET/CT findings. Patients were followed up once at 3 months. The primary outcome was change in planned management after PET/CT and was assessed independently and in duplicate by external outcome adjudicators using all available source documents. Results: 101 patients (mean age 64 y, 45% male, median 1.3 y since last treatment) were enrolled from 4 centers in Ontario, Canada between April 2009 and June 2011. Distribution of tumor types was: non-small cell lung (55%), breast (19%), ovarian (10%), esophageal (6%), lymphoma (6%), head and neck (4%). 8 patients did not complete the study (non-adherence to protocol, 2; death, 5; disease progression prior to PET/CT, 1), of whom 2 did not receive PET/CT. PET/CT changed planned management in 52 (53%) patients (Table). At 3 months, planned management was carried out in 46/52 (88%) patients. Conclusions: In patients with suspected cancer recurrence, PET/CT changes planned management from non-treatment to treatment for approximately 1 in every 3 patients (“number needed to scan” = 3) and contributes importantly to clinical management. [Table: see text]