Description

The morbidity and mortality of malignant tumors are increasing. It is one of the major diseases that affect human health. At present, the conventional imaging diagnosis methods of a variety of malignant tumors are mainly CT and MRI based on anatomical imaging. Different from traditional imaging methods to visually display the lesion, nuclear medicine molecular imaging can not only locate the tumor location, but also image the expression and activity of specific molecules and biological processes. This molecular imaging method integrating anatomy and function is a noninvasive imaging to realize the early diagnosis and differential diagnosis, curative effect evaluation and follow-up observation of a variety of tumors. Positron emission tomography/computed tomography (PET/CT) uses specific molecular probes to target tumor. It can provide detailed information about the biochemical changes of tumor tissues at the cellular and molecular levels. It has better sensitivity and specificity than conventional imaging methods. At present, the most commonly used imaging agent in clinic is 18F-fluorodeoxyglucose (18F-FDG). 18F-FDG PET/CT is a valuable imaging modality in the management of patients with malignant tumors, but it is not a specific imaging agent for tumor application. The physiological uptake of gastrointestinal tract, infected tissues, or inflammatory cells can cause high 18F-FDG uptake resulting in a significant increase of the false positive rate; in addition, some tumors including well-differentiated hepatocellular carcinoma, renal cell carcinoma, and gastric signet ring cell carcinoma have low 18F-FDG uptake resulting in a high false negative rate. Therefore, it is very important to develop new molecular probes for targeting tumor.

Fibroblast-activation protein (FAP) is a type Ⅱ transmembrane serine protease and is overexpressed in cancer-associated fibroblasts (CAFs). CAFs are the predominant component in the stroma of epithelial neoplasms. FAP can be detected in various of malignant neoplasms and is associated to tumor cell migration, invasion, and angiogenesis. Recently, a novel molecular probe, gallium 68-labelled FAP inhibitor (68Ga-FAPI), has been developed and used for visualization of tumor stroma by targeting FAP. Recent studies show favorable diagnosis efficiency in a variety of tumors, especially in gastrointestinal cancer, but the previous studies were all small-sample data or case reports. Therefore, further large-size research is necessary to confirm the advantages of 68Ga-FAPI in various of malignant tumors.