The role of [⁶⁸Ga]Ga-FAP-2286 PET/CT in the evaluation of treatment response in gastrointestinal system malignancies.

OBJECTIVE This study aimed to investigate the potential efficacy of [⁶⁸Ga]Ga-FAP-2286 PET/CT in evaluating treatment response in patients with gastrointestinal system malignancies. MATERIALS AND METHODS Patients with histopathologically confirmed gastrointestinal malignancies who underwent [⁶⁸Ga]Ga-FAP-2286 PET/CT for treatment response assessment between November 2020 and January 2025 were included. All images were evaluated by three experienced nuclear medicine physicians. The maximum standardized uptake values (SUVmax), total tumor volumes, and total lesion FAP expression values of primary tumors and metastases were recorded. At the same time, serum tumor marker levels were analyzed. Imaging responses were assessed separately according to PERCIST criteria on [⁶⁸Ga]Ga-FAP-2286 PET/CT and RECIST criteria on CT. Survival outcomes were analyzed using the Kaplan-Meier method, and their association with treatment response on [⁶⁸Ga]Ga-FAP-2286 PET/CT was assessed using the Log-Rank (Mantel-Cox) test and Cox proportional hazards regression. A p-value < 0.05 was considered statistically significant in all analyses. RESULTS A total of 100 [⁶⁸Ga]Ga-FAP-2286 PET/CT scans were performed in 50 patients (mean age: 61.62 ± 12.95), both before and after treatment. Among the included patients, 70% had gastric cancer, 14% had colon cancer, 8% had pancreatic cancer, 4% had appendiceal cancer, 2% had hepatocellular carcinoma (HCC), and 2% had cholangiocellular carcinoma. Primary/recurrent tumor lesions were observed in 62% of patients, lymph node metastases in 24%, visceral metastases in 10%, peritoneal metastases in 76%, and bone metastases in 14%. A strong correlation was found between tumor volumes and total lesion FAP expression measured by [⁶⁸Ga]Ga-FAP-2286 PET/CT and the corresponding serum tumor markers (Area Under the Curve [AUC] for delta tumor volume and total lesion FAP expression = 0.875). There was a statistically significant and near-perfect concordance between [⁶⁸Ga]Ga-FAP-2286 PET PERCIST and CT RECIST criteria (Kappa = 0.833, p < 0.05). Moderate agreement was found for primary tumors (Kappa = 0.526, p < 0.05) and bone metastases (Kappa = 0.657, p < 0.05), while excellent agreement was observed for lymph node (Kappa = 1.0, p < 0.05), peritoneal (Kappa = 0.815, p < 0.05), and visceral metastases (Kappa = 1.0, p < 0.05). According to the Kaplan-Meier analysis, treatment response assessed by [⁶⁸Ga]Ga-FAP-2286 PET/CT was predictive of overall survival (p = 0.02). Median overall survival was 7.6 months in patients with progressive disease and 19.8 months in those with stable disease, as defined by PERCIST criteria. Median survival was not reached in patients showing partial or complete response. CONCLUSION In gastrointestinal system malignancies, a strong correlation was observed between serum tumor markers and both total tumor volumes and total lesion FAP expression values derived from [⁶⁸Ga]Ga-FAP-2286 PET imaging. Additionally, molecular response assessed by [⁶⁸Ga]Ga-FAP-2286 PET/CT was predictive of overall survival. [⁶⁸Ga]Ga-FAP-2286 PET/CT appears to be an effective tool for assessing treatment response and monitoring patients with gastrointestinal malignancies.