Liver transplantation (LT), including deceased-donor liver transplantation (DDLT) and living-donor liver transplantation (LDLT), has been successfully used to treat hepatocellular carcinoma (HCC) by curing both the tumor and cirrhosis.1-3 4,5 6 6-8
The glucose metabolism of HCC is related to tumor grade and aggressive biological properties and can be assessed with F-18 fluorodeoxyglucose positron emission tomography (FDG-PET).9-12
There is growing evidence that FDG-PET can identify patients at risk of HCC recurrence after LT.13-18 19 15 max ) to normal-liver SUVmax was the most significant predictor for tumor recurrence. The primary aim of this retrospective study was to investigate whether the degree of FDG uptake is associated with HCC recurrence after LDLT. The secondary aim was to explore whether a combination of FDG-PET and morphologic UCSF criteria is able to predict the risk of HCC recurrence after LDLT.
MATERIALS AND METHODS
Patients
Between July 2006 and October 2014, 392 patients with HCC underwent LDLT at Kaohsiung Chang Gung Memorial Hospital. The detailed decision-making for primary resection, locoregional therapy (LRT), or LDLT has previously been described.2
FDG-PET/CT Study and Semiquantification of FDG Uptake Level
After the patients had fasted for at least 6 hours, they were intravenously injected with FDG (range, 70-444 MBq). Thereafter, they stayed calmly in supine position for 1 hour in an isolated room. An integrated PET/CT scanner (Discovery ST; GE Healthcare, Waukesha, WI) was used to acquire images. Computed tomography images were acquired first without contrast medium using the following parameters: 140 kV, 170 mA (maximum), and a 3.75-mm-thick section for attenuation correction and subsequent image fusion. PET scans were then taken from the mid-thigh to the vertex with 7-bed positions of 5 minutes each. The transaxial PET data were reconstructed using an ordered-subset expectation maximization algorithm (2 iterations, 30 subsets) as 128 × 128-pixel images and a slice thickness of 3.27 mm. Coronal and sagittal sections, and PET maximum intensity projection images, were also reformatted for PET/CT image fusion and interpretation. Standardized uptake value was calculated as (decay-corrected radioactivity per unit volume) / (injected FDG radioactivity per body weight). The SUVmax of the HCC was obtained by manually placing a circular region of interest at the highest activity of the tumor. The tumor to nontumor ratio (TNR) was calculated as (tumor SUVmax )/(nontumor SUVmean ), where the nontumor SUVmean was the average of the SUVmean at 3 circular regions of interest (3 cm in diameter) in nontumor liver tissue. F-18 fluorodeoxyglucose–positive HCC on PET/CT was visually interpreted based on its significantly higher uptake than the surrounding nontumor liver tissue and supported by a TNR greater than 1.20.
Immunosuppressive Protocol and Follow Up After LDLT
Basiliximab (Simulect; Novartis Pharma AG, Basel, Switzerland) 20 mg was intravenously administered twice 6 h after portal vein reperfusion and on post-LDLT day 4. Steroid therapy consisted of intraoperative intravenous methylprednisolone (500 mg) followed by 20 mg/day (switched to oral prednisolone 20 mg/day once the patient could tolerate oral medication), which was tapered to zero mg/day after 3 months if no acute cellular rejection occurred. Patients with HCV were not given intraoperative methylprednisolone; they were maintained on low-dose (5 mg/day) prednisolone for 1 to 2 years. Patients who showed stable vital signs and renal function were given tacrolimus (Prograf; Fujisawa, Kerry, Ireland) at a dose to maintain trough levels at 5 to 10 ng/mL during the first week after LDLT. In addition, mycophenolate mofetil (CellCept; Roche, Humacoa, Puerto Rico) was continuously administered at 0.5 to 1 mg/day. Doppler ultrasound was frequently used during the immediate posttransplant period. Patients with HCC underwent CT with volumetry 6 months after LDLT and abdominal ultrasound every 3 months. Liver function, hemograms, biochemistry tests, AFP, and immunosuppressant levels were checked monthly after LDLT.
Statistical Analysis
Categorical variables are expressed as percentages, and continuous values are expressed as means ± SD or median and IQR if data were not normally distributed. Student t test or Mann-Whitney U test was used to compare continuous variables between groups as appropriate. Fisher exact test or χ2 was used to compare categorical variables as appropriate. Time of RFS was defined as the interval between the date of LDLT and the date when recurrence was detected by follow-up imaging modalities. Patient deaths unrelated to HCC recurrence were censored during the statistical analysis of HCC recurrence. The cumulative RFS was assessed using the Kaplan-Meier method, and the differences between groups were analyzed using the log-rank test. Cox proportional hazards regression model was used to assess predictors of RFS. Hazard ratios (HRs, crude and adjusted) and corresponding 95% confidence intervals (CIs) were calculated. The correlation between SUVmax and TNR was evaluated with Pearson correlation analysis. Receiver operating characteristic (ROC) curve analysis was performed using nonparametric method. Given the specificity value, the optimal cutoff values with the highest sensitivity for SUVmax and TNR were found. Internal validation using nonparametric bootstrapping method for SUVmax and TNR was also done. Significance was set at P less than 0.05. SPSS 18 for Windows (SPSS Inc., Chicago, IL) was used for all statistical analyses.
RESULTS
Patient Characteristics and Association With FDG-PET
The enrolled 147 patients (125 men, 22 women) were 55.1 ± 7.4 years of age (range, 29.3-70.5 years). The median follow-up after LDLT was 25.8 months (IQR, 33.2 months). There were 117 patients with negative FDG-PET studies and 30 patients with FDG-positive HCC in the liver. Patients' demographic characteristics and histopathology results of explanted liver according to FDG-PET are shown in Tables 1 and 2 , respectively. The FDG-positive status was significantly associated with tumor differentiation, T stage, mVI, and Milan criteria.
TABLE 1: Patient demographics and pretransplant clinical characteristics according to FDG-PET
TABLE 2: Histopathology results of explanted liver according to FDG-PET
HCC Recurrence and Risk Factor Analysis
Hepatocellular carcinoma recurred in 18 patients (12.2%) at a median of 10.9 months after LDLT (IQR, 11.2 months). Seven patients had intrahepatic recurrence, and 17 patients had extrahepatic recurrence (combined intrahepatic and extrahepatic recurrence in 6 patients). The extrahepatic sites of HCC recurrence were lung (n = 11), lymph nodes (n = 4), bone (n = 4), peritoneum (n = 3), and adrenal gland (n = 2). Of the 117 patients who were FDG-negative, 9 (7.7%) had recurrent HCC at a median of 16.1 months (IQR, 16.9 months), and of the 30 patients who were FDG-positive, 9 (30.0%) had recurrent HCC at a median of 8.1 months (IQR, 4.1 months). Recurrence in the FDG-positive group was earlier than that in the FDG-negative group (P = 0.003). In univariable analysis, T stage (beyond T2), presence of mVI, being FDG-positive, and the semiquantitative parameters of SUVmax and TNR were significant predictors for worse RFS (Table 3 ).
TABLE 3: Cox hazards analysis for recurrence-free survival
Association Between FDG Uptake Level and HCC Recurrence
In the subgroup of 30 FDG-positive patients, the SUVmax and TNR of tumor were 4.6 ± 1.3 and 2.0 ± 0.7, respectively. The correlation between SUVmax and TNR was extremely high (r = 0.971, P < 0.001). Both of the SUVmax and TNR demonstrated acceptable discrimination for predicting HCC recurrence with areas under ROC curve of 0.706 and 0.720, respectively (Figure 1 ). The optimal cutoff values of SUVmax and TNR were 4.8 and 2.0, respectively. To further stratify the risk of HCC recurrence, we used a TNR of 2.0 to divide FDG-positive patients into high (n = 9, TNR ≥ 2) and low (n = 21, TNR < 2) FDG uptake groups. The high FDG uptake was a strong predictor for worse RFS (crude HR, 13.52; 95% CI, 4.77-38.29, P < 0.001), whereas low FDG uptake was not a significant predictor (crude HR, 1.92; 95% CI, 0.52-7.12; P = 0.328).
FIGURE 1: The receiver operating characteristic curve analyses for predicting HCC recurrence. Area under curve of SUVmax was 0.706, and the optimal cutoff value was 4.8 (A). Area under curve of TNR was 0.720, and the optimal cutoff value was 2.0 (B).
HCC Recurrence Associated With Pretransplant LRT
Fifty-five patients were initially beyond clinical UCSF criteria, and they underwent pretransplant LRT (TAE only, n = 18; RFA only, n = 4; TAE and RFA, n = 23; TAE and PEI, n = 5; TAE, RFA, and PEI, n = 5) to downstage to fit UCSF criteria. Their recurrence rate was 16.4% (Table 4 ). Of the 92 patients within clinical UCSF criteria, 67 patients underwent pretransplant LRT (TAE only, n = 27; RFA only, n = 17; PEI only, n = 1; TAE and RFA, n = 19; TAE and PEI, n = 1; TAE, RFA, and PEI, n = 2), and their recurrence rate was 7.5% (Table 4 ). In the 25 patients without pretransplant LRT, their recurrence rate was 16.0% (Table 4 ).
TABLE 4: Recurrence rates based on combination of FDG-PET and UCSF criteria (Clinical and Pathologic)
HCC Recurrence Rates According to FDG-PET and Clinical UCSF Criteria
The recurrence rates associated with FDG-PET and UCSF criteria are shown in Table 4 . In patients within clinical UCSF criteria and negative FDG-PET, the recurrence rate was low at 5.2%. In patients beyond clinical UCSF criteria after tumor downstaging with LRT and post-LRT negative FDG-PET, the recurrence rate was 12.5%. In patients with low FDG uptake (FDG-positive, TNR < 2) HCC, their recurrence rates were 11.1% (within clinical UCSF criteria) and 16.7% (beyond clinical UCSF criteria after tumor downstaging). In patients with high FDG uptake (TNR ≥ 2) HCC, the recurrence rates were 66.7% (both within and beyond UCSF criteria). Therefore, the risk of HCC recurrence can be divided into 3 groups using a combination of FDG-PET and clinical UCSF criteria. Patients within UCSF criteria and negative FDG-PET were the low-risk group (n = 77, recurrence rate 5.2%). Intermediate-risk group (n = 61, recurrence rate 13.1%) included patients beyond clinical UCSF criteria after downstaging and negative FDG-PET, and patients with low FDG uptake HCC. Patients with high FDG uptake HCC were the high-risk group (n = 9, recurrence rate 66.7%).
HCC Recurrence Rates According to FDG-PET and Pathologic UCSF Criteria
The concordance rate between the pretransplant clinical UCSF status and pathologic UCSF status was 80.3%. In patients within pathologic UCSF criteria and negative FDG-PET, the recurrence rate was low at 3.6%. In patients beyond pathologic UCSF criteria and negative FDG-PET, the recurrence rate was 17.6%. In patients with low FDG uptake (FDG-positive, TNR < 2) HCC, their recurrence rates were 16.7% (within pathologic UCSF criteria) and 11.1% (beyond pathologic UCSF criteria). In patients with high FDG uptake (TNR ≥ 2) HCC, the recurrence rates were 66.7% (both within and beyond UCSF criteria). Using a combination of FDG-PET and pathologic UCSF criteria, the HCC recurrence rates were 3.6% (3/83), 16.4% (9/55), and 66.7% (6/9) in low-, intermediate-, and high-risk groups, respectively.
RFS According to FDG-PET, UCSF Criteria, and Combination of FDG-PET and UCSF Criteria
The estimated 1-, 3-, and 5-year RFS were 97.2%, 90.5%, and 84.8%, for the FDG-negative group, and 72.3%, 68.3%, and 68.3%, for the FDG-positive group, respectively (P < 0.001, Figure 2 A). When the FDG-positive group was divided into high and low FDG uptake groups, the high FDG uptake group had the worst RFS (1 year, 44.4%; and 3 and 5 years, 29.6%; vs the low FDG uptake group, P = 0.005; vs the FDG-negative group, P < 0.001). However, there was no significant difference (P = 0.337) between the low FDG uptake (1, 3, and 5 years, 85.0%) and the FDG-negative groups (Figure 2 B). The estimated 1-, 3-, and 5-year RFS were 94.3%, 89.6%, and 83.6%, for the patients within clinical UCSF criteria, and 88.7%, 79.6%, and 79.6%, for the patients beyond clinical UCSF criteria after tumor downstaging (P = 0.286, Figure 2 C). According to the combination of FDG-PET and clinical UCSF criteria, the estimated 1-, 3-, and 5-year RFS were 100%, 94.1%, and 85.5% in the low-risk group; 89.9%, 83.9%, and 83.9% in the intermediate-risk group (vs the low-risk group, P = 0.142); and 44.4%, 29.6%, and 29.6% in the high-risk group (vs the low-risk group, P < 0.001; vs the intermediate-risk group, P < 0.001, Figure 2 D). The estimated 1-, 3-, and 5-year RFS were 93.8%, 89.1%, and 89.1%, for the patients within pathologic UCSF criteria, and 88.5%, 79.3%, and 69.4%, for the patients beyond UCSF criteria (P = 0.076, Figure 2 E). According to the combination of FDG-PET and pathologic UCSF criteria, the estimated 1-, 3-, and 5-year RFS were 100%, 94.0%, and 94.0% in the low-risk group; 88.6%, 83.4%, and 75.8% in the intermediate-risk group (vs the low-risk group, P = 0.013); and 44.4%, 29.6%, and 29.6% in the high-risk group (vs the low-risk group, P < 0.001; vs the intermediate-risk group, P < 0.001, Figure 2 F).
FIGURE 2: Kaplan-Meier analyses of recurrence-free survival according to FDG-PET positivity (A), FDG uptake level (B), clinical UCSF criteria (C), combination of FDG-PET and clinical UCSF criteria (D), pathologic UCSF criteria (E), and combination of FDG-PET and pathologic UCSF criteria (F).
In univariable analysis, the high-risk (crude HR, 19.41; 95% CI, 5.44-69.18; P < 0.001) group according to FDG-PET and clinical USCF criteria, and both of the intermediate-risk (crude HR, 4.56; 95% CI, 1.23-16.86; P = 0.023) and high-risk (crude HR, 28.74; 95% CI, 7.14-115.71; P < 0.001) groups according to FDG-PET and pathologic UCSF criteria were significant predictors for worse RFS. In multivariable analysis (T-stage, mVI, and combination of FDG-PET and pathologic UCSF criteria), only the high-risk group (adjusted HR, 24.15; 95% CI, 5.76-101.23; P < 0.001) was a significant independent predictor associated with a worse RFS (Table 3 ).
DISCUSSION
In the present study, being FDG-positive was a significant predictor for worse RFS. Our results, as well as those of other published studies, support the notion that positive FDG uptake predicts HCC recurrence after LT. Yang et al13 14 16
Lee et al17
In addition to FDG positivity, our study demonstrated that the degree of FDG uptake was associated with HCC recurrence and contributed to stratify the risk of HCC recurrence after LDLT. We evaluated the semiquantitative parameters of SUVmax and TNR and found that both of them were significant predictors. The optimal cutoff values of SUVmax and TNR were 4.8 and 2.0, respectively. The cutoff values in our study are higher than those in the Lee study.15 max to normal-liver SUVmax (TSUVmax /LSUVmax ), tumor SUVmax to normal-liver SUVmean (TSUVmax /LSUVmean ), and SUVmax were 1.15, 1.35, and 3.0, respectively. Their study demonstrated that TSUVmax /LSUVmax had largest area under curve in ROC analysis and its cutoff value of 1.15 was the most effective prognostic factor in the prediction of tumor recurrence. In our study, the 2 parameters, SUVmax and TNR, were highly correlated and their areas under curve in ROC analysis were similar. Because SUV measurements are prone to be influenced by a variety of biologic and technologic factors, including scanner and reconstruction parameters,20 max to stratify the risk of HCC recurrence.
Our data indicated that high FDG uptake (TNR ≥ 2) on a PET scan was a stronger predictor than FDG positivity. High FDG uptake had a greater effect than did low FDG uptake (TNR < 2) on worse RFS (HR, 13.52 vs 1.92), and the difference of RFS was not significant between patients with low FDG uptake tumors and FDG-negative tumors. It has also been reported that high FDG uptake (SUV ≥ 5 or TNR ≥ 2) in HCC is associated with tumor aggressiveness and poor survival after a liver resection or LRT.21-24 9,10,25 26 12,26,27 12,26
Hepatocellular carcinoma recurrence after LT is believed to be the result of undetected occult metastases before transplantation or from the engraftment of circulating tumor cells released at the time of transplantation.28 29 30
Although an FDG-PET study is widely used to assess extrahepatic metastasis from HCC,31-34
In conclusion, our study demonstrated that FDG-positive HCC is a predictor for HCC recurrence after LDLT. Recurrence is earlier after LDLT in patients with FDG-positive HCC. Moreover, SUVmax and TNR, the semiquantitative parameters for FDG uptake level, are also significantly associated with recurrence. High FDG uptake (TNR ≥ 2) is a strong predictor for HCC recurrence after LDLT. Combination of FDG-PET and UCSF criteria can be used to predict the risk of HCC recurrence after LDLT.
ACKNOWLEDGMENTS
The authors would like to thank Man-Jen Hsu, PhD (Clinical Trial Center, Kaohsiung Chang Gung Memorial Hospital) for assistance with statistical analysis.
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