Comparative study of 18F-FAPI-04 and 18F-FDG PET/CT in the initial staging and postoperative metastasis detection of gastric cancer

Table 1 Baseline patient characteristics of the study patients

Description of patients	n (%)
Age
> 60	18 (85.7)
≤ 60	3 (14.3)
Gender
Female	4 (19.0)
male	17 (81.0)
Primary tumors	11 (52.4)
LR or metastases	10 (47.6)
LNM	8 (38.1)
BM	2 (9.5)
LM	1 (4.8)
PM	6 (28.6)

LR: Local recurrences; LNM: Lymph node metastases; BM: Bone metastases; LM: Liver metastases; PM: Peritoneal metastases.

Table 2 Comparison of ¹⁸F-fibroblast activation protein inhibitor-04 and ¹⁸F-fluorodeoxyglucos uptake in various lesions

Descriptions of lesions	18F-FAPI-04 PET/CT				18F-FDG PET/CT				P value FAPI/FDG
	SUVmax	FTV (cm3)	TLF (SUVbw × cm3)	TBR	SUVmax	MTV (cm3)	TLG (SUVbw × cm3)	TBR	SUVmax	TBR	F/MTV	TLF/G
Primary GC	11.6 (10.5-19.3)	41.2 (17.9-69.9)	260.5 (131.6-363.1)	11.5 (10.5-17.4)	6.5 (5.0-8.1)	18.4 (8.6-27.9)	57.9 (30.9-126.8)	5.1 (4.6-7.4)	0.036	0.009	0.088	0.036
LNM	6.6 (4.4-10.6)	3.1 (0.8-3.4)	8.3 (2.6-20.9)	5.4 (4.2-9.2)	6.5 (3.8-10.5)	1.9 (0.5-3.3)	6.3 (2.1-16.2)	6.4 (4.5-9.6)	0.703	0.65	0.321	0.654
BM	11.1 (9.0-16.6)	6.4 (3.2-14.8)	27.7 (12.5-84.2)	10.4 (8.4-16.0)	5.5 (4.5-6.7)	2.4 (0.9-13.1)	9.5 (2.8-52.5)	5.6 (4.0-7.0)	< 0.001	< 0.001	0.128	0.045
PM	7.1 (4.7-10.0)	13.2 (3.4-25.5)	39.3 (16.2-76.8)	7.4 (5.8-9.7)	3.2 (0.0-3.9)	1.2 (0.0-1.8)	3.3 (0.0-5.3)	2.4 (0.0-3.9)	0.002	0.002	0.003	0.004
LM	8.4 (7.4-9.3)	15.2 (10.3-20.1)	67.6 (43.7-91.5)	9.8 (8.7-10.9)	8.2 (8.1-8.2)	8.0 (6.3-9.7)	35.3 (27.9-42.8)	7.4 (6.9-7.8)	N/A	N/A	N/A	N/A
LR	3.9 (NA)	7.8 (NA)	24.7 (NA)	8.1 (NA)	2.9 (NA)	1.2 (NA)	3.2 (NA)	1.2 (NA)	N/A	N/A	N/A	N/A

¹⁸F-FAPI-04: ¹⁸F-fibroblast activation protein inhibitor-04; PET/CT: Positron emission tomography/computed tomography; ¹⁸F-FDG: ¹⁸F-fluorodeoxyglucose; FAPI: Fibroblast activation protein inhibitor; FDG: Fluorodeoxyglucose; SUVmax: Maximum standardized uptake value; FTV: Fibroblast activation protein inhibitor-avid tumor volume; TLF: Total lesion fibroblast activation protein expression; SUVbw: Standardized uptake value normalized to body weight; TBR: Tumor-to-background ratio; MTV: Fluorodeoxyglucose-derived metabolic tumor volume; TLG: Total lesion glycolysis; F/MTV: Fibroblast activation protein inhibitor-avid tumor volume/fluorodeoxyglucose-derived metabolic tumor volume; TLF/G: Total lesion fibroblast activation protein expression/total lesion glycolysis; GC: Gastric cancer; LR: Local recurrences; LNM: Lymph node metastases; BM: Bone metastases; LM: Liver metastases; PM: Peritoneal metastases; NA: Not available (data could not be calculated due to only 1 lesion in the local recurrences group); N/A: Not applicable (statistical comparisons were not performed for lesion types with fewer than 3 lesions i.e., liver metastases and local recurrences subgroups).

Table 3 Comparison of ¹⁸F-fibroblast activation protein inhibitor-04 and ¹⁸F-fluorodeoxyglucos in diffuse peritoneal metastatic lesions

Characteristics	FAPI		FDG		P value
	Median range		Median range
PCI	14	6-25	2.5	2-3	0.012
SUVmax	8.0	5.7-13.0	4.7	3.5-5.8	0.001
Characteristics	Primary tumors	LNM	BM	PM	LM
18F-FAPI-04	19	32	65	30	3
18F-FDG	17	25	36	6	2

PCI: Peritoneal cancer index; LR: Local recurrences; LNM: Lymph node metastases; BM: Bone metastases; LM: Liver metastases; PM: Peritoneal metastase; FAPI: Fibroblast activation protein inhibitor; FDG: Fluorodeoxyglucos; SUVmax: Maximum standardized uptake value; ¹⁸F-FAPI-04: ¹⁸F-fibroblast activation protein inhibitor-04; ¹⁸F-FDG: ¹⁸F-fluorodeoxyglucos.

Table 4 Diagnostic performance of ¹⁸F-fibroblast activation protein inhibitor-04 and ¹⁸F-fluorodeoxyglucos uptake in various lesions

Lesions	Tracer	No. of TP	No. of TN	No. of FN	Sen (%)	95%CI	NPV (%)
Primary tumors	18F-FAPI-04	11	0	0	100%	0.717-1.0	N/A
	18F-FDG	10	0	1	90.9%	0.623-0.984	N/A
LNM	18F-FAPI-04	8	1	0	100%	0.678-1.0	100%
	18F-FDG	6	1	2	75%	0.409-0.928	33.3%
BM	18F-FAPI-04	1	0	1	N/A	N/A	N/A
	18F-FDG	1	0	1	N/A	N/A	N/A
PM	18F-FAPI-04	6	0	0	100%	0.610-1.0	N/A
	18F-FDG	3	0	3	50%	0.188-0.812	N/A
LM	18F-FAPI-04	1	0	1	N/A	N/A	N/A
	18F-FDG	1	0	1	N/A	N/A	N/A
LR	18F-FAPI-04	1	0	0	N/A	N/A	N/A
	18F-FDG	1	0	0	N/A	N/A	N/A

¹⁸F-FAPI-04: ¹⁸F-fibroblast activation protein inhibitor-04; ¹⁸F-FDG: ¹⁸F-fluorodeoxyglucos; CI: Confidence interval; TP: True positive; TN: True negative; FN: False negative; NPV: Negative-predictive value; Sen: Sensitivity; LR: Local recurrences; LNM: Lymph node metastases; BM: Bone metastases; LM: Liver metastases; PM: Peritoneal metastases; N/A: Not applicable. Sensitivity not reported because only 1 true positive case was identified for this lesion type; any calculated sensitivity (50% or 100%) would be statistically unstable and clinically uninformative.