Utility of 99m Tc-PEG 4 -E[PEG 4 -c(RGDfK)] 2 in Posttherapy Surveillance of Patients with Reelevated Carcinoembryonic Antigen Levels

Objectives: To evaluate the efficacy of 99m Tc-PEG 4 -E[PEG 4 -c (RGDfK)] 2 ( 99m Tc-3PRGD2) single photon emission computed tomography (SPECT) in monitoring the recurrence of malignancies. Materials and Methods: 99m Tc-3PRGD2 SPECT was performed on 28 patients (10 females and 18 males; median age 49.2 years) suspected of recurrent malignancies due to an asymptomatically reelevated carcinoembryonic antigen level. The SPECT was performed 0.5 h after an intravenous injection of 11.1 MBq/kg (0.3 mCi/kg) of 99m Tc- 3PRGD2. The SPECT and concurrent contrast-enhanced computed tomography (ceCT) findings were analyzed with reference to the histopathological findings and/or clinical follow-up data. Results: Recurrences were identified in 20 out of the 28 patients (prevalence 71.4%) with altogether 26 lesions. Fifteen lesions were confirmed by histopathological findings, and the other 11 lesions were confirmed by serial radiological or clinical follow-up. Of the 20 patients with recurrent malignancies, 12 (60%) were correctly identified by 99m Tc-3PRGD2 SPECT. In the patient-based analysis, the sensitivity and specificity of 99m Tc-3PRGD2 SPECT were 60 and 100%, respectively, and the positive and negative predictive values were 100 and 50%, respectively. In the lesion-based evaluation, the sensitivity and specificity were 62 and 100%, respectively. The sensitivity and specificity of the ceCT in the patient-based evaluation were 60 and 75%, respectively, and the positive and negative predictive values were 86 and 40%, respectively. In the lesion-based evaluation, the sensitivity and specificity of the ceCT were 70 and 84%, respectively. Conclusions: 99m Tc-3PRGD2, as a new SPECT tracer targeting the integrin αvβ3 receptor, was more useful in distinguishing recurrences as compared to ceCT.