Patient Characteristics
This study included a total of 33 patients (19 men and 14 women; median age, 61 years; interquartile range, 54–71 years) who were evaluated and treated for primary CRC between October 2021 and June 2022. The diagnosis of the primary CRC lesions was confirmed by pathological examination, with 15 (45.5%) diagnosed as colon cancer and 18 (54.5%) as rectal cancer. Of the 33 patients, 10 (30.3%) had T3 stage, 23 had T4 stage (69.7%), but none had T1 and T2 stage; 9 (27.3%), 12 (36.4%), 9 (27.3%), and 3 (9.1%) patients had N0, N1, N2, and Nx stages, respectively. Twenty-one (63.6%) patients had M0 stage, whereas 12 patients had M1 stage (36.4%). Twenty-six patients had the KRAS gene, including 13 patients with mutated KRAS and 13 patients with wild-type KRAS. The details of the patient characteristics are summarized in Table 1.
Table 1
Summary of patient characteristics.
|
Value
|
No. of patients
|
33
|
Age (years)
|
|
Median
|
61
|
Interquartile range
|
54–71
|
Sex
|
|
Men
|
19
|
Women
|
14
|
Tumor location
|
|
Colon
|
15
|
Rectum
|
18
|
AJCC-TNM
|
|
Ⅱ
|
7
|
Ⅲ
|
14
|
Ⅳ
|
12
|
T stage
|
|
T3
|
10
|
T4
|
23
|
N stage
|
|
N0
|
9
|
N1
|
12
|
N2
|
9
|
Nx
|
3
|
M stage
|
|
M0
|
21
|
M1
|
12
|
KRAS status
|
|
Mutated type
|
13
|
Wild type
|
13
|
Adverse Events
All the patients tolerated the [68Ga]Ga-FAPI PET/CT examination. There were no signs of any [68Ga]Ga-FAPI-related pharmacologic effects or physiological responses. None of the patients reported abnormal symptoms.
Relationship Between T Stage and FAPI Parameters in CRC
The SUVmax, SUVmean, TL-FAPI, and GTVFAPI values were calculated in patients with different T statuses (Figure 1). Our multivariate analysis revealed that SUVmax30%, SUVmax40%, SUVmax50%, SUVmax60%, SUVmean30%, SUVmean40%, and SUVmean50% values were statistically correlated with T status (p=0.025, 0.025, 0.028, 0.038, 0.018, 0.042, and 0.047, respectively; Table 2). No significant difference in TL-FAPI and GTVFAPI according to the TNM status was found (Table 3).
Table 2
Measurements of standardized uptake values in patients with colorectal carcinoma.
|
SUVmax with percent threshold method
|
|
SUVmean with percent threshold method
|
|
30%
|
40%
|
50%
|
60%
|
|
30%
|
40%
|
50%
|
60%
|
T3
|
8.44 (8.14, 10.12)
|
8.46 (8.05, 10.24)
|
8.45 (8.12, 10.28)
|
8.45 (8.10, 10.50)
|
|
4.78 (4.46, 5.13)
|
5.58 (5.01, 6.31)
|
5.94 (5.46, 6.91)
|
6.5 (5.92, 7.55)
|
T4
|
10.52 (8.59, 11.85)
|
10.58 (8.77, 11.91)
|
10.64 (8.65, 11.88)
|
10.64 (8.68, 11.98)
|
|
5.48 (4.63, 6.41)
|
6.24 (5.29, 6.98)
|
7.01 (5.78, 7.66)
|
7.81 (6.28, 8.58)
|
p-value
|
0.025
|
0.025
|
0.028
|
0.038
|
|
0.018
|
0.042
|
0.047
|
0.081
|
Table 3
Measurements of GTVFAPI and TL-FAPI in patients with colorectal carcinoma.
|
TL-FAPI with percent threshold method
|
|
GTVFAPI with percent threshold method
|
|
30%
|
40%
|
50%
|
60%
|
|
30%
|
40%
|
50%
|
60%
|
T3
|
111.33 (51.95, 161.51)
|
84.93 (42.69, 115.22)
|
68.68 (34.56, 89.44)
|
49.74 (24.85, 57.05)
|
|
21.89 (10.78, 35.42)
|
15.68 (7.78, 19.55)
|
11.71 (5.82, 13.41)
|
7.30 (3.84, 8.45)
|
T4
|
209.36 (42.47, 397.79)
|
112.77 (33.15, 335.31)
|
75.85 (25.52, 279.92)
|
46.7 1 (19.09, 182.89)
|
|
29.63 (9.50, 77.98)
|
16.26 (6.59, 57.76)
|
10.82 (4.58, 41.09)
|
6.21 (3.14, 21.18)
|
p-value
|
0.221
|
0.287
|
0.305
|
0.428
|
|
0.550
|
0.499
|
0.603
|
0.603
|
Relationship Between N stages and FAPI Parameters in CRC
Out of the 33 patients with CRC, 9 (27.3%), 12 (36.4%), 9 (27.3%), and 3 (9.1%) had N0, N1, N2, and Nx stages, respectively. The SUVmax30%, SUVmax40%, SUVmax50%, SUVmax60%, SUVmean30%, SUVmean40%, SUVmean50%, SUVmean60%, TL-FAPI30%, TL-FAPI40%, TL-FAPI50%, TL-FAPI60%, GTVFAPI30%, GTVFAPI40%, GTVFAPI50%, and GTVFAPI60% values in patients with different N statuses were calculated (all p>0.05, p=0.488, 0.530, 0.524, 0.516, 0.432, 0.332, 0.431, 0.579, 0.791, 0.840, 0.893, 0.926, 0.652, 0.561, 0.601, and 0.747, respectively).
Relationship Between M stages and FAPI Parameters in CRC
Twenty-one (63.6%) patients had M0 stage disease, whereas 12 (36.4%) had M1 stage disease. The SUVmax30%, SUVmax40%, SUVmax50%, SUVmax60%, SUVmean30%, SUVmean40%, SUVmean50%, SUVmean60%, TL-FAPI30%, TL-FAPI40%, TL-FAPI50%, TL-FAPI60%, GTVFAPI30%, GTVFAPI40%, GTVFAPI50%, and GTVFAPI60% values in patients with different M statuses were not significantly different (p>0.05, p=0.258, 0.228, 0.213, 0.242, 0.427, 0.308, 0.326, 0.258, 0.811, 0.839, 0.839, 0.927, 0.754, 0.868, 0.927, and 0.985, respectively).
Predictive Performance of FAPI Parameters for T Stage
ROC curves of SUVmax30%, SUVmax40%, SUVmax50%, SUVmax60% as well as SUVmean30%, SUVmean40%, and SUVmean50% were derived from FAPI PET/CT images for predicting the T stage in patients with CRC. The AUCs for predicting T3 from T4 were 0.748, 0.748, 0.743, and 0.730 for SUVmax30%, SUVmax40%, SUVmax50%, and SUVmax60%, respectively. In addition, the AUCs were 0.761, 0.726, and 0.722 for SUVmean30%, SUVmean40%, and SUVmean50%. The cutoff values for predicting T3 from T4 were 8.802, 8.758, 8.809, and 8.986 for SUVmax30%, SUVmax40%, SUVmax50%, and SUVmax60%, respectively. In addition, the cutoff values were 5.275, 5.596, and 6.086 for SUVmean30%, SUVmean40%, and SUVmean50%. Regarding the predictive performance of FAPI PET/CT parameters for T status, SUVmean30% demonstrated the highest predictive performance among the metabolic parameters (p<0.050), with an AUC of 0.761 (95% CI: 0.591–0.931), a sensitivity of 67.4% (95% CI: 0.472–0.681), and a specificity of 90.0% (95% CI: 0.557– 0.796). The detailed predictive performance of the PET/CT parameters and their ROC curves are illustrated in Table 4 and Figure 2.
Table 4
Predictive performance of metabolic parameters.
Parameters
|
AUC (95% CI)
|
Optimal cutoff value
|
Sensitivity (95% CI)
|
Specificity (95% CI)
|
SUVmax30%
|
0.748 (0.575, 0.921)
|
8.802
|
0.587 (0.468, 0.678)
|
0.70 (0.555, 0.781)
|
SUVmax40%
|
0.748 (0.572, 0.924)
|
8.758
|
0.587 (0.467, 0.679)
|
0.70 (0.555, 0.780)
|
SUVmax50%
|
0.743 (0.563, 0.924)
|
8.809
|
0.609 (0.465, 0.678)
|
0.75 (0.554, 0.775)
|
SUVmax60%
|
0.730 (0.546, 0.915)
|
8.986
|
0.587 (0.461, 0.674)
|
0.70 (0.546, 0.765)
|
SUVmean30%
|
0.761 (0.591, 0.931)
|
5.274
|
0.674 (0.472, 0.681)
|
0.90 (0.557, 0.796)
|
SUVmean40%
|
0.726 (0.546, 0.906)
|
5.596
|
0.587 (0.462, 0.672)
|
0.70 (0.539, 0.767)
|
SUVmean50%
|
0.722 (0.542, 0.901)
|
6.086
|
0.587 (0.461, 0.669)
|
0.70 (0.535, 0.765)
|