Evaluation of 68Ga-FAPI PET/CT and 18F-FDG PET/CT for the diagnosis of recurrent colorectal cancers

Objective: The present study aimed to compare the diagnostic value of gallium-68-labeled fibroblast activation protein inhibitor positron emission tomography/computed tomography (Ga-68-FAPI PET/CT) and fluorine-18-labeled fluorodeoxyglucose PET/CT (F-18-FDG PET/CT) for detecting recurrent colorectal cancers (CRCs). Materials and Methods: Fifty-six patients (age: 18-80 years, 31 men and 25 women) with suspected recurrent CRC were enrolled and underwent F-18-FDG PET/CT and Ga-68-FAPI PET/CT sequentially within 1 week. The maximum standard uptake value (SUVmax), tumor-to-background ratio (TBR), and diagnostic accuracy were estimated and compared between the two modalities by using Student's t-test. The Wilcoxon signed-rank test was used to compare peritoneal carcinoma index (PCI) scores between the two imaging modalities. Results: Ga-68-FAPI PET/CT showed higher sensitivity for detecting recurrence (93 % vs. 79 %); lymph node metastasis (89 % vs. 78 %), particularly peritoneal lymph node metastasis (92 % vs. 63 %); and metastatic implantation on the intestinal wall (100 % vs. 25 %) compared to F-18-FDG PET/CT. However, Ga-68-FAPI PET/CT showed lower sensitivity for detecting bone metastasis (67 % vs. 100 %). The mean SUVmax values of peritoneal metastases and metastatic implantation on the intestinal wall were 4.28 +/- 2.70 and 7.58 +/- 1.66 for F-18-FDG PET/CT and 5.66 +/- 1.97 and 6.70 +/- 0.25 for Ga-68-FAPI PET/CT, respectively. Furthermore, Ga-68-FAPI PET/CT showed significantly higher TBR for peritoneal metastatic lesions (4.22 +/- 1.47 vs. 1.41 +/- 0.89, p < 0.0001) and metastatic implantation on the intestinal wall (5.63 +/- 1.24 vs. 2.20 +/- 0.5, p = 0.02) compared to F-18-FDG PET/CT. For the same patient, Ga-68-FAPI PET/CT yielded a more accurate PCI score and a greater area under the curve value for the receiver operating characteristic curve (p < 0.01) than F-18-FDG PET/CT. Conclusion: Ga-68-FAPI PET/CT was superior to F-18-FDG PET/CT for detecting recurrence and peritoneal metastases. Hence, we propose the combination of these two modalities for better clinical diagnosis and management of patients with CRC.