Circulating tumor cells (CTC), [18F]fluorodeoxyglucose positron emission tomography, and computed tomography (PET/CT) for treatment monitoring in patients with metastatic breast cancer (MBC)

Abstract

e12007 Background: Use of [18F]-fluorodeoxyglucose PET /CT and/or CTC is being investigated to follow up response to treatment in patients with MBC. It is not clear if these tests can be a surrogate for one another. Methods: We retrospectively analyzed a database of female patients with MBC undergoing chemotherapy or hormonal therapy. Most of these patients received at least 2 lines of therapy. Standard CT scan tumor measurements were used to assess response to therapy. CTC were defined either low (0–5) or high (>5). Maximum standard uptake values (max SUV) on PET scan were defined either low (<3) or high (>3). Correlation between the max SUV and CTC counts was statistically analyzed. Sensitivity, specificity, positive and negative predictive values were calculated from 2 x 2 table. Results: A total of 9 female patients with MBC were identified (mean age of 52 years). The receptor status of these patients includes 67 % positive for ER and 33 % positive for HER-2/neu. Median follow up was 9.8 months. There were 59 time points (> or = 4 weeks apart) when either PET/CT or CTC were performed. The results of PET/CT scans were compared with CTC at 38 events. The sensitivity of CTC to detect metastatic disease shown on PET/CT was 32% and specificity of 100%. The positive and negative predictive values were 100% and 32% respectively. There was a positive correlation between the max SUV and CTC count (p = 0.001). However in three patients, despite of progression of disease per PET/CT, CTC were undetectable at three different time points. Interestingly, two out of these three patients were triple negative. Disease progression was confirmed by biopsy in two of these patients. Conclusions: Our data suggest positive correlation between PET/CT scan and CTC. However, CTC had poor sensitivity and negative predictive value to detect progressive metastatic disease. Normal CTC values have to be interpreted cautiously in patients with MBC. We are now planning to investigate the utility of these tests, prospectively, in a large cohort of MBC patients. No significant financial relationships to disclose.