Preoperative [68Ga]Ga-FAPI-04 PET for evaluating pathological complete response to neoadjuvant therapy in gastrointestinal adenocarcinoma patients

Xiao Zhang^1,2,3Yuan Feng^1,2,3Zhaoguo Lin^1,2,3Ranran Chen⁴Yongkang Gai^1,2,3Chunxia Qin^1,2,3XIAOLI LAN^1,2,3*

• ¹Department of Nuclear Medicine, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
• ²Hubei Key Laboratory of Molecular Imaging, Wuhan, China
• ³Key Laboratory of Biological Targeted Therapy, the Ministry of Education, Wuhan, China
• ⁴Department of Nuclear Medicine, Mindong Hospital, Fujian Medical University, Ningde, China

Objective: This study aimed to assess the value of preoperative [68Ga]Ga-FAPI-04 positron emission tomography (PET) for evaluating pathological complete response (pCR) in patients with gastrointestinal adenocarcinomas receiving neoadjuvant therapy (NAT). Materials and Methods: A retrospective analysis was conducted on patients with gastrointestinal adenocarcinomas who received [68Ga]Ga-FAPI-04 PET/MR scans between February 2021 and January 2024. The enrolled patients had completed preoperative NAT, undergone contemporary enhanced CT or MR scans, and received surgery within one month after PET imaging. Clinical data, imaging evaluations, PET parameters (standardized uptake values [SUVs], SUVs standardized by lean body mass [SUL], FAPI-positive tumor volume [FAPI-PTV], and total lesion burden [FAPI-TL]), and surgical pathology results were collected. Each parameter's sensitivity, specificity, and diagnostic cutoff for predicting pCR were determined via receiver operating characteristic curve analysis. Logistic regression analysis identified independent predictors of pCR. Results: Sixty-five patients were enrolled, and 22 patients achieved pCR according to surgical pathology. In visual evaluation, [68Ga]Ga-FAPI-04 PET was limited in its ability to assess pCR, with 16 false positives and 1 false negative. The dichotomization using the FAPI-PTV cutoff value (<1.92 cm3) improved the specificity for predicting pCR to 72.7%, while retaining a high sensitivity of 93.0%. Enhanced CT or MR scans had the sensitivity and specificity of 72.7% and 93.0% in predicting pCR, respectively. According to the logistic regression analysis, a FAPI-PTV<1.92 cm3 was an independent predictor for patients who achieved a pCR (p<0.05). Conclusion: [68Ga]Ga-FAPI-04 PET shows promise in predicting pCR among patients with gastrointestinal adenocarcinomas following NAT. FAPI-PTV derived from [68Ga]Ga-FAPI-04 PET may provide an effective clinical tool for guiding further treatment.