Efficacy of 18F-FDG PET/CT in investigation of elevated CEA without known primary malignancy

Aim: To evaluate the efficacy of ¹⁸flurodeoxyglucose positron emission tomography/computer tomography (¹⁸F-FDG PET/CT) in investigating patients with elevated carcinoembryonic antigen (CEA) and without known primary malignancy, and the impact of PET/CT findings on patient management.

Setting and design: PET/CT scans done in a tertiary hospital between December 2007 and February 2012 for elevated CEA in patients without known primary malignancy were retrospectively reviewed.

Materials and methods: The PET/CT findings, patients' clinical information, level of CEA, histological diagnosis, and subsequent management were retrieved by the electronic patient record for analysis.

Statistical analysis: Data were analyzed using SPSS version 19.

Results: One hundred and one PET/CT scans were performed for patients with elevated CEA. Fifty-eight of these were performed for patients with known primary malignancy and were excluded; 43 PET/CT scans were performed for patients without known primary malignancy and were included. Thirty-three (77%) had a positive PET/CT. Among the 32 patients with malignancy, 15 (47%) suffered from lung cancer and 8 (25%) suffered from colorectal cancer. The sensitivity (97%), specificity (82%), positive predictive value (94%), negative predictive value (90%), and accuracy (93%) were calculated. Thirty (91%) patients had resultant change in management. The mean CEA level for patients with malignancy (46.1 ng/ml) was significantly higher than those without malignancy (3.82 ng/ml) (P < 0.05). In predicting the presence of malignancy, a CEA cutoff at 7.55 ng/ml will achieve a sensitivity of 91% and a specificity of 73%.

Conclusion: PET/CT, in our study population, appears to be sensitive, specific, and accurate in investigating patients with elevated CEA and without known primary malignancy. In addition to diagnosis of underlying primary malignancy, PET/CT also reveals occult metastases which would affect patient treatment options. Its role in investigating patients with elevated CEA and without known primary, compared with other investigation modalities, remains to be studied.