Keywords
hepatocellular carcinoma - Radiofrequency ablation - recurrence
Introduction
Percutaneous Radiofrequency ablation (RFA) or microwave ablation (MWA) has an important
role in treatment early hepatocellular carcinoma (HCC) size less than 3 cm because
of its effectiveness, feasibility, and less complications.[1]
[2] There are two types of intrahepatic recurrence found in patients with HCC after
RFA, including local tumor progression (LTP) and intrahepatic distant recurrence (IDR).
LTP occurs along the peripheral margin of the low attenuated ablation zone, while
IDR is a new HCC tumor remote from the margin of the original ablation zone.
Although these ablation therapies can achieve complete necrosis of small HCC, recurrence
is still common. The 3-year LTP rates for patients treated by RFA with an ablation
margin of 0.5 to 1.0 cm are reportedly 10 to 20%. The risk factors for tumor recurrence
after RFA included tumor size, located near the main portal branch or inferior vena
cava, elevated α fetoprotein level, platelet count, and antihepatitis C antibody positivity.[3]
[4]
[5]
[6]
[7]
Several studies believe tumor hypoxia and hepatic parenchymal hypoperfusion after
RFA are significant predictive factors of tumor recurrence. After RFA, the transition
zone between normal liver tissues and ablation zone exposes residual cancer cells
to a hypoxic microenvironment. The hypoxia-inducible factors (HIF) are active via
hypoxic signaling pathway. It causes tumor cells to become more invasive, metastatic,
chemoresistant resulting to intrahepatic recurrent.[8]
[9] Lee et al reported that hepatic parenchymal hypoperfusion caused by either ischemia
resulting from portal vein injury or congestion from hepatic vein damage after RFA
is a significant predictive factor of recurrence after RFA of a single nodular HCC.[10]
We propose that large ablative volume might be associated with tumor hypoxia and hepatic
parenchymal hypoperfusion. It may induce vascular endothelial growth factor and cause
intrahepatic tumor recurrence. The aim of this study was to compare recurrence-free
survival between patients who had large ablative volume and small ablative volume.
Materials and Methods
Diagnosis of HCC
According to Liver Reporting & Data System (LI-RADS) and American Association for
the Study of Liver Diseases guideline, patients with liver mass compatible with LI-RADS
4 and LI-RADS 5 were enrolled in this study.
Study Design and Patient Population
Patients with HCC treated with RFA between 2015 and 2017 was 283 visits. The inclusion
criteria were as follows: patients with LI-RADS 4 or 5, single lesion, size less than
3.0 cm, Barcelona Clinic Liver Cancer stage 0 or A, patients should have a complete
response at the first follow-up images at 4 to 8 months and underwent follow-up computed
tomography (CT) every 3 to 6 months. We excluded patients with a history of previous
treatment of HCC and the presence of other malignancies. Finally, 50 patients were
included.
This retrospective cohort study was approved by the institute research committee and
informed consent was waived (Approval no. RAD-2562–0649).
RFA Protocol
RFA was performed by using ultrasound-guided percutaneous puncture with the multitined
expandable electrode (LeVeen Needle Electrodes; Boston Scientific Cooperation, United
States). We used 1-cm stepwise expansion of the tines and double ablation method until
the tines were fully expanded.[11] All patients underwent follow-up CT scans or magnetic resonance imaging (MRI) 4
weeks after RFA. The goal of the treatment was to achieve complete ablation in the
tumor ablation zones, which were the hypoattenuating unenhanced areas in the arterial
and the portal venous phases that were larger than the previous tumor.
Measurement Technique and Parameters
The size of the lesion was measured at the greatest diameter and calculated the tumor
volume by using Syngo.via application (Siemens Healthineers, United States) in arterial
phase. The ablation zone was measured at the greatest diameter and calculated the
ablative volume by using Syngo.via application in portovenous phase.
Ablative margin was classified into two groups: closed ablative margin (margin < 0.5cm)
and large ablative margin (margin > 0.5 cm). To define the ablative margin as accurate
as possible, we performed qualitative side-by-side comparison of CT scans obtained
before and after RF ablation by a radiologist with 12 years of experience. The adjacent
hepatic vessels or the hepatic capsule were used to facilitate comparison.[12]
The ideal ablative volume was calculated by 4/3 x π x (D/2 + 0.5)[3] under the assumption of spherical shape and 0.5-cm safety ablative margin.[13]
[14] When ablative volume was anywhere larger than ideal ablative volume, we defined
as large ablative volume. While ablative volume was smaller than ideal ablative volume,
we defined as small ablative volume. The ratio between ablative volume and ideal ablative
volume was defined as ablative volume ratio.
All patients underwent follow-up CT every 3 to 6 months. The recurrent date was defined
as the date that CT or MRI demonstrated tumor recurrence. Recurrent was classified
as LTP or IDR. The endpoint of nonrecurrent group used the last CT or MRI date in
Picture Archiving and Communication System.
Statistical Analyses
Statistical analyses were proceeded by SPSS software (version 24) and Stata (version
15.1). Descriptive data with normal distribution are reported as mean ± standard deviation
(SD). The difference between two groups was compared using Student's t-test or the Mann–Whitney test. The cumulative recurrent rate during the follow-up
was recorded. Recurrence-free survival curve was estimated by the Kaplan–Meier method
and statistically significant was compared with the Log-Rank test. Multivariate analysis
using the stepwise cox proportional hazard model was performed for the variable with
p <0.10 in the univariate analysis to investigate independent risk factors for tumor
recurrence.
Results
Patients' population, tumor, and ablative parameters were shown in [Table 1]. There was no significant difference in baseline characteristics between the recurrence
and nonrecurrence groups. The follow-up ranged from 1 to 48 months. Twenty-two patients
developed tumor recurrence after treatment including 6 LTP and 16 IDR. The recurrence-free
survival rate in first, second, third, and fourth years after RFA were 83, 56, 44,
and 44%, respectively. The recurrence-free survival curve was shown in [Fig. 1].
Table 1
Baseline characteristics of all patients, patients with recurrence, patient without
recurrence, LTP, and IDR
|
All
(n = 50)
|
Recurrent
(n = 22)
|
Nonrecurrent
(n = 28)
|
p-Values
|
|
Age (y)[a]
|
60.6 ± 10.3
|
58.82 ± 10.19
|
61.93 ± 10.34
|
|
|
Sex (%)
|
|
Male
|
38(76)
|
18 (36)
|
20(40)
|
0.512
|
|
Female
|
12(24)
|
4(8)
|
8(16)
|
|
BCLC stage (%)
|
|
0
|
31(62)
|
13(26)
|
18(36)
|
0.774
|
|
A
|
19(38)
|
9(18)
|
10(20)
|
|
Child–Pugh (%)
|
|
A
|
40(80)
|
17(34)
|
23(46)
|
0.732
|
|
B
|
10(20)
|
5(10)
|
5(10)
|
|
Hepatitis B (%)
|
26(52)
|
13(26)
|
13(26)
|
0.407
|
|
Hepatitis C (%)
|
18(36)
|
9(18)
|
9(18)
|
0.565
|
|
Tumor size (cm)[a]
|
1.80 ± 0.56
|
1.87 ± 0.56
|
1.75 ± 0.58
|
0.493
|
|
Tumor volume (cm3)[a]
|
3.25 ± 2.72
|
3.84 ± 2.99
|
2.81 ± 2.47
|
0.192
|
|
Ablation size (cm)[a]
|
2.99 ± 2.33
|
3.32 ± 3.45
|
2.72 ± 3.33
|
0.599
|
|
Ablation volume (cm3)[a]
|
12.22 ± 8.40
|
12.36 ± 7.69
|
12.11 ± 9.06
|
0.250
|
|
Ablation margin (cm)[a]
|
0.36 ± 0.35
|
0.36 ± 0.37
|
0.37 ± 0.34
|
0.005
|
|
Ablation margin more than 0.5cm (%)
|
19(38)
|
8(16)
|
11(22)
|
1.00
|
|
Ablation volume more than ideal ablation volume (%)
|
47(94)
|
20(40)
|
27(54)
|
0.576
|
|
Ablation volume/Ideal ablation volume ratio
|
5.98 ± 8.13
|
7.10 ± 11.24
|
5.10 ± 4.46
|
0.547
|
Abbreviation: BCLC, Barcelona Clinic Liver Cancer; IDR, intrahepatic distant recurrence;
LTP, local tumor progression; SD, standard deviation.
a Present in mean ± SD.
Fig. 1 Recurrence-free survival curve in patients underwent Radiofrequency ablation, in
all patients (A), local tumor progression, (B) and intrahepatic distant recurrence (C).
The recurrence-free survival time in large ablative margin was slightly longer than
closed ablative margin (33.29 vs. 28.28 months, p = 0.201). Patients with large ablative volume showed a significantly longer recurrence-free
survival time than small ablative volume (31.57 vs. 8.50 months, p = 0.003; [Fig. 2]).
Fig. 2 (A) Comparison of recurrence-free survival between closed ablative margin (blue) and
large ablative margin (green), which shows average 28.28 and 33.29 months, respectively.
(B) Comparison of recurrence-free survival between small ablative volume (blue) and
large ablative volume (green), which shows average 8.50 and 31.57 months, respectively.
In the univariate analysis, the potential factors for tumor recurrence after RFA were
α-fetoprotein level, tumor size, tumor volume, and large ablative volume ([Table 2]). These four factors were further analyzed with multivariate analysis. Only large
ablative volume was an independent risk factor for tumor recurrence after RFA (hazard
ratio [HR]= 0.12, 95% confidence interval [CI] = 0.02–0.84, p = 0.033).
Table 2
Logistic regression of the risk factor associated overall tumor recurrence
|
Variable
|
Univariate analysis
|
Multivariate analysis
|
|
HR (95%CI)
|
p-Value
|
HR (95%CI)
|
p-Value
|
|
Age (y)
|
0.98(0.95–1.02)
|
0.543
|
|
|
|
Sex (female/male)
|
0.68(0.23–2.02)
|
0.494
|
|
|
|
BCLC stage (0/A)
|
1.60(0.68–3.77)
|
0.274
|
|
|
|
Child–Pugh (A/B)
|
0.97(0.35–2.64)
|
0.960
|
|
|
|
Albumin level
|
0.92(0.53–1.62)
|
0.790
|
|
|
|
AFP level
|
1.00(1.00–1.00)
|
0.010
|
1.00 (0.99–1.01)
|
0.099
|
|
LI-RADS (5/4)
|
1.41(0.41–4.78)
|
0.578
|
|
|
|
Tumor size (cm)
|
2.29(0.93–5.63)
|
0.070
|
0.67(0.10–4.70)
|
0.691
|
|
Tumor volume (cm3)
|
1.31(1.10–1.56)
|
0.002
|
1.288(0.86–1.93)
|
0.219
|
|
Arterial enhancement (N/Y)
|
1.89(0.25–14.14)
|
0.533
|
|
|
|
Portal washout (N/Y)
|
1.71(0.22–12.92)
|
0.602
|
|
|
|
Capsule enhancement (N/Y)
|
0.88(0.38–2.03)
|
0.761
|
|
|
|
Ablation time (min)
|
0.99(0.95–1.04)
|
0.909
|
|
|
|
Ablation size (cm)
|
1.06(1.93–1.21)
|
0.342
|
|
|
|
Ablation volume (cm3)
|
0.99(0.95–1.04)
|
0.891
|
|
|
|
Ablation margin (cm)
|
0.51(0.15–1.65)
|
0.263
|
|
|
|
Ablation margin more than 0.5 cm (N/Y)
|
0.57(0.24–1.37)
|
0.209
|
|
|
|
Ablation volume more than ideal ablation volume (N/Y)
|
0.14(0.03 - 0.64)
|
0.011
|
0.12(0.02–0.84)
|
0.033
|
|
Ablation volume /Ideal ablation volume ratio
|
1.00(0.95 -1.05)
|
0.853
|
|
|
Abbreviations: AFP, α-fetoprotein; BCLC, Barcelona Clinic Liver Cancer; CI, confidence
interval; HR, hazard ratio; LI-RADS, Liver Imaging Reporting and Data System.
The univariate and multivariate analysis for LTP and IDR were shown ([Table 3]).
Table 3
Logistic regression of the risk factor associated LTP and IDR
|
LTP
|
IDR
|
|
Variable
|
Univariate analysis
|
Multivariate analysis
|
Univariate analysis
|
Multivariate analysis
|
|
HR (95% CI)
|
p-Value
|
HR (95% CI)
|
p-Value
|
HR (95% CI)
|
p-Value
|
HR (95%CI)
|
p-Value
|
|
AFP level
|
1.01(0.995–1.017)
|
0.252
|
|
|
1.00(1.00–1.01)
|
0.018
|
1.00(0.99–1.01)
|
0.146
|
|
Tumor size (cm)
|
3.91(0.62–24.61)
|
0.146
|
|
|
1.92(0.68–5.41)
|
0.218
|
|
|
|
Tumor volume (cm3)
|
1.32(0.91–1.90)
|
0.140
|
|
|
1.31(1.08–1.60)
|
0.007
|
1.24(1.00–1.54)
|
0.045
|
|
Ablation time (min)
|
0.94(0.82–1.08)
|
0.378
|
|
|
1.01(0.96–1.06)
|
0.669
|
|
|
|
Ablation size (cm)
|
1.16(0.99–1.34)
|
0.058
|
1.24(1.04–1.48)
|
0.017
|
0.93(0.63–1.39)
|
0.726
|
|
|
|
Ablation volume (cm3)
|
0.94(0.83–1.07)
|
0.389
|
|
|
1.01(0.96–1.06)
|
0.706
|
|
|
|
Ablation margin (cm)
|
0.51(0.54–4.88)
|
0.562
|
|
|
0.51(0.13–2.02)
|
0.339
|
|
|
|
Ablation margin more than 0.5 cm (N/Y)
|
0.48(0.09–2.65)
|
0.399
|
|
|
0.61(0.22–1.685)
|
0.22
|
|
|
|
Ablation volume more than ideal ablation volume (N/Y)
|
0.02(0.00–0.18)
|
0.001
|
0.007(0.0–0.124)
|
0.001
|
2.27(0)
|
1.0
|
7.58(0)
|
1.0
|
|
Ablation volume /Ideal ablation volume ratio
|
0.76(0.51 -1.11)
|
0.162
|
|
|
1.02 (0.97–1.06)
|
0.382
|
|
|
Abbreviations: AFP, α-fetoprotein; CI, confidence interval; HR, hazard ratio; IDR,
intrahepatic distant recurrence; LTP, local tumor progression.
Independent risk factors of LTP were ablation size (HR =1.24, 95% CI = 1.04–1.48,
p = 0.017) and large ablative volume (HR = 0.007, 95% CI = 0.0–0.124, p = 0.001).
An independent risk factor of IDR was tumor volume (HR =1.24, 95% CI = 1.00–1.54,
p = 0.045). The HR for large ablative volume cannot be analyzed because all of the
patients with IDR had large ablative volume.
Discussion
The overall recurrence-free survival rate in our study was similar to the prior study,
which shows a recurrence-free survival rate at first and third years ∼74 and 40%,
respectively.[15]
Several studies tried to describe the risk factor for tumor recurrence especially
ablative margin. The ablative margin less than 0.5 cm has a higher risk for tumor
recurrence after RFA.[13] In our study, we had a higher recurrence-free survival rate in large ablative margin
than closed ablative margin, but it is not significant (p = 0.201). Furthermore, we found some patients had HCC adjacent to the liver capsule
or vascular structures. These patients were described as a 0-mm ablative margin, but
the tumor recurrence did not occur. So, the ablative margin was not the good parameter
to predict the recurrence-free survival rate. Ablative volume may be another parameter
use to predict tumor recurrence. We found that patients with large ablative volume
had a significantly higher recurrence-free survival rate than small ablative volume
(p = 0.03).
Large ablative volume may produce hypoxic microenvironment and causes tumor recurrence.
Lee et al proposed hepatic parenchymal hypoperfusion after RFA as a significant predictive
factor of recurrence.[10] We believe larger ablative volume could induce more HIF and play a role to develop
intrahepatic tumor recurrence.
To balance between recurrent from inadequate margin and hypoxic microenvironment,
we focus on ablative volume ratio instead of ablative volume. From our data, 94% of
patients had ablative volume more than ideal ablation volume. The average ablative
volume was six times greater than ideal ablative volume, ablative volume ratio. Patient
who had tumor recurrence had ablative ratio larger than the nonrecurrent group. The
IDR patients had a higher ablation ratio; up to 8.6 time. Therefore, we presume the
ablation volume ratio was the other predictive factor for tumor recurrent, especially
IDR.
There are several limitations of this study. First, it was retrospective that caused
variety of biases. Therefore, further studies are required in a prospective trial.
Second, the measurement of ablation margin by side-by-side comparison technique by
one radiologist may not be consistent. Test of observer agreement such as interobserver
reliability by two radiologists should be analyzed in the further studies. Additional,
in some previous studies, they try to use intelligent software for fused pre- and
post-treatment imaging.[13]
[16] It had more accuracy for evaluating the ablation margin than manual registration,
but it was not available in our department.
We concluded that a large ablative volume was the independent factor for predicting
higher intrahepatic recurrence-free survival and decreased risk of LTP. Conversely,
a large ablative volume with high ablative ratio might increase risk of IDR.
