Study populations
A search was conducted in a prospectively maintained LT database between January, 2000 and December, 2018. Among 332 patients undergoing LT for HCC, 81 patients without bridging procedures, 139 patients treated with other locoregional therapy [radiofrequency ablation (RFA), TACE+RFA and percutaneous ethanol injection (PEI)] and 6 patients receiving hepatic resection prior to LT were excluded. We also excluded 40 patients without pre- and/or post-TACE imaging. The final study population consisted of 66 patients treated only with TACE (Figure 1). Diagnosis of HCC was made on histologic or radiologic criteria according to published guidelines [16] and confirmed on explant histopathology analysis. Percutaneous biopsy for diagnosis of HCC was not routinely performed.
In patient recruitment, the Milan Criteria was used as the primary indication of LT for HCC, in accordance with institution policy. After confirmation of diagnosis, patients supposed to be within the Milan Criteria were immediately listed for LT. LRT was performed in patients beyond Milan Criteria at initial imaging for downstaging, or in patients within Milan Criteria, but with an expected waiting time for bridging of more than 2 months. Those exceeding the Milan Criteria were listed after LRT if the treatment resulted in stable diseases or partial response according to the mRECIST criteria at 3 month intervals. Pre-transplant LRT include conventional TACE, RFA, TACE plus RFA, and percutaneous ethanol injection (PEI). TACE has been employed as a first line therapy in the patients with extensive disease burden (largest tumor size >3cm and/ or tumor number > 3). Percutaneous radiofrequency ablation (RFA) is mainly used in lesions measuring≤3cm. Patients were excluded from TACE if they had decompensated cirrhosis (Child-Pugh B, score >8), severely reduced portal vein flow, extensive tumor with massive replacement of both lobes, renal insufficiency (creatinine ≥2 mg/dL or creatinine clearance ≤30 mL/min) and untreatable arterio-venous fistula [17]. In all cases, data from both the initial CT investigation and the last CT scan after TACE before LT, if available, were evaluated.
CT Technique and image evaluation
The pre- and post TACE multiphasic contrast enhanced studies of the enrolled subjects were performed on multidetector computed tomography (MDCT) scanners (ranging from 8 to 64 rows of detectors), with 0.6-1.5 -mm collimation, 3 -mm slice interval and 3-5 -mm slice thickness. Patients were scanned before and after the intravenous administration of iodine contrast media in the arterial phase, portal-venous phase and equilibrium phase. The studies were retrospectively reviewed on commercially available workstations (MV1000, Siemens Healthcare, and IMPAX, Agfa Healthcare) simultaneously by two expert abdominal radiologists, who were unaware of the explant histopathology findings.
The largest diameter of the enhancing portion of the lesions on pre-TACE CT scan was measured in the imaging phase in which the lesion was best seen, and only lesions greater than or equal to 1 -cm were included in the study. The HCC attenuation in each phase was classified as hyper-attenuation, iso-attenuation or hypo-attenuation, when compared with the surrounding liver parenchyma. A lesion with heterogeneous enhancement was regarded as hyper-attenuating when most of it was enhanced during the arterial phase compared with the pre-contrast phase. Hyper-attenuation on the arterial phase followed by washout in the portal or equilibrium phase was defined as “typical enhancement”. A hypo-attenuated area with no change in the degree of attenuation during the dynamic phase was defined as necrosis. The shape of the tumor margin was categorized into three subgroups: smooth; lobulated or infiltrative. Capsule appearance means a rim of hyper-enhancement in portal, delayed, or transitional phase, which is unequivocally thicker than fibrotic tissue around background nodules [18].
HCC lesions were classified in three major categories based on their pattern of enhancement and margins. Type A: Well-defined (or circumscribed) tumors with arterial phase hyper enhancement (relative to the background liver parenchyma) and portal-venous or equilibrium phase wash-out. Type B: Well-defined (or circumscribed) tumors with arterial phase iso- or hypo enhancement (relative to the background liver parenchyma) and portal-venous or equilibrium phase wash-out. Type C: Poorly defined (or infiltrative) tumors, irrespective of their enhancement pattern.
CT follow-up was performed 1 month after TACE, and at least every 3 months until LT. The post-TACE CT scan images performed prior to the liver transplant were subsequently reviewed in the same session and compared side-by-side with the pre-TACE CT scan, in order to assess the treatment response. The responses to TACE were categorized according to the mRECIST [19] as follows: complete response (CR), which included the disappearance of any intratumoral arterial enhancement; partial response (PR), which displayed a ≥30% decrease in the diameter of the viable portion (enhancement in the arterial phase) of a target lesion (taking the baseline diameter of the target lesion as a reference); progressive disease (PD), which was defined as a ≥20% increase in the diameter of the viable portion of a target lesion (taking as reference the baseline diameter of the target lesion); and stable disease (SD), which included any cases not categorized as PR or PD.
TACE protocol
TACE was performed after patients provided written informed consent. 5-F catheters or 3-F coaxial microcatheters were inserted into the common femoral artery and angiographic survey of the celiac and superior mesenteric arteries was performed. Common hepatic angiography was performed to determine tumor blood supply, and then a microcatheter was selectively inserted into the artery feeding the tumor. We selected epirubicin (Pharmorubicin, Pfizer; Wuxi, Jiangsu, China) as the anticancer drug for suspending in Lipiodol. Epirubicin (20-40mg) was dissolved in 2 mL saline and suspended in the adapted amount of Lipiodol (2–10 ml) (Guerbet, Roissy, France). The emulsion was injected into the supplying artery until stop of flow. Under fluoroscopic guidance, the vessels were subsequently embolized with Gelfoam (ALICON Pharm SCI &TEC CO., Hangzhou, China) until complete flow stagnation was achieved. The interventional radiologist chose the amount of the chemotherapeutic and embolic agents depending on the tumor size, number of tumors, tumor arterial blood supply, degree of liver impairment, and renal function. Repeat TACE treatment was typically scheduled in patients with adequate hepatic function reserve (Child-Pugh A or Child-Pugh B <8) and residual viable tumor at 6 to 8 week intervals after the initial treatment. In contrast, in patients with no evidence of residual viable disease (i.e., with CR according to mRECIST), imaging follow-up was recommended every 2 to 3 months. If PR or SD was achieved, the patients were administered with the same chemotherapeutic agent. If progressive disease (PD) occurred, the chemotherapeutic agent was adjusted to cisplatin or lobaplatin.
Histopathology:
After transplantation, an experienced hepatopathologist performed the gross and histologic analyses of all explanted livers. The freshly explanted livers were sliced serially at 10-mm intervals. Routine hematoxylin and eosin staining were used to prepare the slides. The number, size, location and gross characteristics of all lesions were assessed. The grade of differentiation was based on the Edmondson and Steiner criteria (grade 1, well differentiated; grade 2, moderately differentiated; grade 3, poorly differentiated). The presence of lymphovascular invasion was recorded. If heterogeneous differentiation was found in the obtained tumor, differentiation grade was classified based on the lowest differentiated grade. The presence of partial necrosis was assessed by the pathologist as the percentage of necrotic tissue divided by total tumor tissue. A necrosis of 100% was assumed to indicate complete necrosis.
Statistical Analysis:
Continuous variables were expressed as means and standard deviations, medians and ranges, or both. Categorical variables were reported as numbers and percentages. Pearson’s chi-square tests or Fisher’s exact tests were performed to evaluate categorical variables and the Student’s t-test for continuous data. Continuous variables were transformed into binary variables and the cutoffs were chosen according to previous studies. After univariate analysis, only variables that emerged as significant were used in the multivariate analysis using Cox’s proportional hazard model. Sensitivity, specificity, positive (PPV) and negative (NPV) predictive values, and accuracy of CT in the detection of 100% necrosis were calculated. A two-tailed P-value of <0.05 was considered to be statistically significant. Statistical analyses were performed with SPSS 22.0 (SPSS, Inc., Chicago, IL) for Windows.