To investigate the ability of the CLDN18.2-targeted 68Ga-PMD22 tracer to detect CLDN18.2 expression in patients with gastric and colorectal cancer and other gastrointestinal tumours.

The 2016 FAST study brought a "new star" target for gastric cancer - CLDN18.2 (claudin 18 splice variant 2,CLDN18.2), which belongs to the CLDN family of tight junction proteins and is involved in the formation of paracellular tight junctions and maintenance of cell polarity. CLDN18.2 is mainly found in the normal gastric mucosa (normal gastric glands, principal cells, mural cells, endocrine cells) where the differentiation cycle is short and renewal is rapid, and in the duodenal panniculocytes, but not in the gastric stem cell region. It is now generally accepted that CLDN18.2 is expressed in normal gastric tissue confined to the tight junctions at the outer base of the gastric mucosal cells, whereas tumours undergo a change in cell polarity during malignant transformation, resulting in widespread exposure of CLDN18.2 to the cell membrane surface. The CLDN18.2 gene is also aberrantly activated and highly specific and stably expressed in specific tumour tissues, participating in the proliferation, differentiation and migration of tumour cells, making it a potentially effective target for anti-tumour drugs.

In this study, a molecular probe PMD22 targeting CLDN18.2 was synthesised in a previous study and a 68Ga-PMD22 injection was developed for clinical trials. The preliminary study showed that the tracer has good safety and good imaging effect. It is proposed to further conduct exploratory PET/CT imaging studies on patients with gastric cancer, colorectal cancer and other gastrointestinal tumours, to provide a new technique for in vivo, non-invasive and visual detection of CLDN18.2 expression level and spatial distribution for patients with gastric cancer, colorectal cancer and other gastrointestinal tumours, and to validate its clinical application value for the diagnosis of gastric cancer, colorectal cancer and other gastrointestinal tumours.

Inclusion Criteria:

• In the near future (within 2 months), patients who plan to undergo puncture biopsy or undergo tumor surgical treatment or are clinically highly suspected of cancer (including primary and tumor recurrence and metastasis)
• Able to understand and voluntarily sign informed consent forms, with good compliance

Exclusion Criteria:

• Severe abnormalities in liver and kidney function
• Suffering from claustrophobia or other mental illnesses
• Pregnant and lactating women