Background: Staging for BR is challenging since the yield of computed tomography (CT) and bone scans are low, especially in patients with low prostate specific antigens (PSA) levels. We examined the utility of circulating tumor cells (CTCs) to predict metastatic disease in a cohort of patients who presented with BR (Aragon-Ching, et. al. ASCO GU 2011;abstr 60). Methods: 33 pts enrolled from May 2010 to September 2011 with BR, defined as patients (pts) who have undergone primary treatment with PSA rise to >/= 0.2 from a prior undetectable level for prior prostatectomy or > 2 mg/dl rise from post-nadir radiotherapy, were included. PSA doubling time (PSADT), scan results, Gleason scores, age, testosterone levels were all obtained. CTCs were evaluated in 7.5 mL of peripheral blood using the CTC CellSearch test. BR patients with equivocal CT and/or bone scan results who were biopsiable and consentable underwent bone biopsy to confirm metastatic disease. Results: The median age for 33 patients was 71 y/o (range: 51 – 91), median PSA of 1.7 ng/mL (range 0.2 – 65.8), testosterone levels of 315.5 ng/dL (range: 31 – 727), Gleason score of 7, hemoglobin of 13.78 g/dL, BMI of 27.72 and alkaline phosphatase of 68 IU/L. Prostatectomy was the primary treatment in 23 pts, radiotherapy in 9 pts and Cyberknife in 1 pt. Median PSADT varied between 0.35 to 55.2 months. Only a small number of patients had either biopsy confirmed metastatic disease (n=2) or detectable CTC (n=3). Both of the 2 patients with metastatic disease had detectable CTC (sensitivity = 1.00, 95% CI: .34, 1.00). For the patients without signs or confirmation of metastatic disease, 30/31 had no detectable CTC (specificity = .97, 95% CI: .84, .99). Conclusions: While most pts with BR have negative blood CTCs, patients with detectable CTCs and equivocal findings on scans should raise suspicion and prompt a search for metastatic disease, given increasing available treatment options for metastatic prostate cancer. However, the limited number of patients may preclude reliable statistical evaluation of CTCs in this population. Supported by IRG-08-091-01 from ACS to GWU Cancer Institute.