JNM: SPECT tracer shines light on lung malignancies

^99mTc-3PRGD2, a new SPECT tracer that targets integrin xvB3 receptor, is sensitive for the detection of lung cancer, according to a study published in the May issue of The Journal of Nuclear Medicine.

Zhaohui Zhu, MD, of the department of nuclear medicine of Peking Union Medical College in Beijing, and colleagues devised a multicenter study to examine the efficacy of ^99mTc-3PRGD2 in the evaluation of patients with lung cancer. Integrin xvB3 receptor is expressed preferentially on various types of tumor cells and activated endothelial cells of tumor angiogenesis, and has emerged as a target for diagnosis and treatment of malignant tumors, according to the researchers.

^99mTC-labeled peptides have shown higher in vitro integrin binding and increased tumor uptake in animal models, providing the impetus for the current study.

The researchers enrolled 51 men and 19 women (mean age 63 years +/- 9 years) with a suspected lung lesion and ultimate definite pathologic diagnosis. A total of 58 patients had malignant tumors and 12 were benign.

Patients were injected with ^99mTc-3PRGD2 and then underwent anterior and posterior planar scans of the whole body and SPECT scans of the chest at one hour and four hours. Six nuclear medicine physicians masked to the source, history and pathologic diagnosis interpreted the studies through consensus reading. CT images were provided as a reference.

The reviewers completed a visual analysis of the lesions and semiquantitative analysis of tumor-to-background (T/B) and tumor-to-mediastinum (T/M) ratios of the whole-body planar and SPECT images.

The researchers reported low background in the lungs and mediastinum, which allowed easy discrimination of thoracic lesions. Most lung malignancies were prominent in the one-hour images, and T/B ratios were significantly lower in benign lesions, according to Zhu et al.

Zhu and colleagues calculated sensitivity of 88 percent for the semiquantitative analysis, which reached 93 to 97 percent in the visual analysis when the volume effect, necrosis and metastasis were considered. However, specificity was relatively low at 58 to 67 percent. Lower uptake in benign lesions might have been related to selection bias of benign conditions, high expressions of integrin xvB3 receptor in inflammatory angiogenesis and other related processes and a small number of benign cases.

Whole-body planar scanning and chest SPECT are complementary, the researchers wrote, and one-hour imaging suffices for diagnosis. Visual analysis may aid semiquantitative assessment, they added.

The researchers noted two advantages associated with ^99mTc-3PRGD2: it is more broadly available than ¹⁸F-labeled tracers and can be prepared via a kit formulation. They also suggested additional potential applications, including evaluation of breast cancer and imaging of brain metastasis from lung cancer.

The results are preliminary, according to Zhu et al. “Further studies are also needed to investigate the correlation between ^99mTc-3PRGD2 uptake and integrin xvB3 expression and to compare the uptake of ^99mTc-3PRGD2 and ¹⁸F-FDG in both tumors and benign lesions.” They added that noninvasive molecular characterization of integrin expression is feasible and may have implications in the development of therapeutics.