Investigation of diffuse non-neoplastic 68Ga-FAPI uptake of pancreas in patients with digestive tract tumors

Introduction: In previous ⁶⁸Ga-FAPI imaging studies, high heterogeneity of diffuse uptake of FAPI tracer in the pancreas of patients with digestive tract tumors was observed. The purpose of this study was to explore the related factors affecting pancreatic diffuse FAPI tracer uptake in patients with digestive tract tumors.

Methods: In this retrospective study, ⁶⁸Ga-FAPI PET images and patient records of 225 patients with digestive tract tumors with diffuse uptake pattern of pancreas were investigated for the correlation between the SUVmax，pancreas-to-liver ratio(PLR) values of pancreatic ⁶⁸Ga-FAPI uptake and characteristics and outcome.

Results: We observed that PLR was negatively correlated with body weight(R=-0.158,P=0.018) and BMI(R=-0.161,P=0.016), while SUVmax was positively correlated with CA125(R=0.197,P=0.004).

In addition, the univariate analysis of SUVmax(7.07±4.57 vs.5.67±3.61,P=0.023) and PLR(4.91±3.40 vs.3.93±3.13,P=0.039) by t-test showed that operation was the influencing factor, while chemotherapy(6.44±4.23 vs.7.06±4.53,P=0.338;4.48±3.23 vs.4.86±3.60,P=0.452) and immunotherapy(6.79±4.38vs.6.50±4.28,P=0.628;4.62±3.57 vs.4.56±3.18,P=0.90) were not. Among them, there was a significant difference in the uptake whether it is surgery with impaired pancreatic structure (such as Whipple operation,14.37±6.57 vs.6.56±3.75,P＜0.001) or surgery with impaired pancreatic function (radical distal gastrectomy or total gastrectomy,10.04±5.24 vs.6.51±3.8,P=0.001;8.37±4.28vs.6.54±3.91,P=0.032), but whether proximal gastrectomy and colorectal surgery were performed or not will not cause the difference in uptake. There was a low negative correlation between SUVmaxp and operation interval (R=-0.166,P=0.043). In addition,we found that there were differences in the factors affecting SUVmax and PLR at different cut-off values(4,5,6).

Conclusions: Pancreatic diffuse ⁶⁸Ga-FAPI uptake in patients with digestive tract tumors is negatively correlated with body weight and positively correlated with CA125 levels. The operating mode is an imaging factor that affects pancreatic uptake, especially pancreatic function and structural destruction. This provides a possible explanation for the diffuse non-neoplastic uptake of FAPI in the pancreas.

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