Correlation among [18F]fluorodeoxyglucose positron emission tomography/computed tomography, cancer antigen 27.29, and circulating tumor cell testing in metastatic breast cancer.

BACKGROUND: Tumor marker cancer antigen (CA) 27.29 and combined [18F]-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT) scans are used to follow up response to treatment and disease progression in patients with metastatic breast cancer (MBC). Recently, circulating tumor cell testing (CTC) has been used in this context. It is not known if 1 of the 3 tests can be a surrogate for another. PATIENTS AND METHODS: We analyzed a database of 35 patients with MBC. There were 173 time points (> or = 6 weeks apart) when > or = 2 of these tests were performed. Correlation among all the 3 tests was statistically analyzed. RESULTS: Results of PET/CT scans were compared with CA 27.29 at 163 time points. There was a statistically significant correlation between both groups (P = .02); however, sensitivity of CA 27.29 to detect metastatic disease observed on PET/CT scan was 59%. The results of PET/CT scans were compared with CTC at 93 events, where there was a statistically significant correlation between both groups (P = .0002); however, sensitivity of CTC to detect metastatic disease shown on PET/CT scans was 55%. Cancer antigen 27.29 results were also compared to CTC at 100 events, where there was a statistically significant correlation between both groups (P = .0002). However, only 64% of patients with high CA 27.29 had abnormal CTC. CONCLUSION: Our data shows correlation among PET/CT scan, CA 27.29, and CTC. However, both CA 27.29 and CTC had poor sensitivity and negative predictive value to detect metastatic disease observed on PET/CT scan. Normal CA 27.29 testing or CTC has to be interpreted cautiously in patients with MBC.