Abstract 430P
Background
Poorly cohesive carcinoma (PCCs) imaging is challenging due to the known limitations of FDG PET-CT. Fibroblast activating protein (FAP) expressing cancer-associated fibroblasts (CAFs) makes a significant component of most epithelial tumors. In recent times, FAP inhibitors (FAPI) have been found to be promising for theranostics in many cancers. Here, we present our initial experience of Ga68 FAPI-46 PET-CT in PCCs stomach compared to FDG PET-CT.
Methods
This is an initial experience of an ongoing prospective open-label single institutional study (RES/SCM/59/2023/54). This data set includes 21 histologically proven stomach PCCs (13 stagings and eight recurrences) with both FAPI and FDG PET-CT available. The single voxel maximum standard uptake value (SUVmax) of the primary, lymph node, metastasis, and the right lobe of the liver were recorded. Histopathological correlation was done for metastasis (M stage) and recurrence accuracy. Wilcoxon's signed-rank test was used to compare SUVmax and target-to-background ratio (TBR), while McNemar’s test was used to compare the diagnostic performance. ROC curve was generated for FAPI to find the best SUVmax cutoff for recurrence prediction.
Results
Out of 13 staging PCCs patients, FDG showed peritoneal metastasis in 3/7 patients with diagnostic sensitivity, specificity, PPV, NPV and accuracy of 42.8%, 100%, 100%, 60%, and 69.2%. Meanwhile, FAPI detected all 7/7 peritoneal metastases with 100% diagnostic accuracy. Mean± SD TBR of primary (1.53±0.53 Vs 7.2±4.65) and node (0.69±0.37 Vs 3.31±3.21) for FDG Vs FAPI showed significant difference (P value <0.05). FDG detected 3/5 while FAPI detected 5/5 recurrence cases and diagnostic sensitivity, specificity, PPV, NPV and accuracy were 60%, 33.3%, 60%%, 33.3%, 50% and 100%, 66.6%, 83.3%, 100%, 87.5% respectively. ROC curve analysis showed the best cutoff of >4.3 SUVmax for FAPI with sensitivity 100% and specificity 66.6% (AUC 0.933, P value <0.001) for recurrence.
Conclusions
FAPI PET-CT was found to have significantly better diagnostic performance for M staging and recurrence for PCCs of the stomach. It may become an imaging standard in tailoring the diagnostic laparoscopy and management of these patients in future.
Legal entity responsible for the study
The authors.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.