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Page 10 of 18 Galicia-Moreno et al. Hepatoma Res 2020;6:20 I http://dx.doi.org/10.20517/2394-5079.2019.36

Pugh C score and HCV co-infection. Currently, Latin America has transplant programs and more than 2500
[8]
liver transplants are performed in the region every year . Worldwide, in 2017, an estimated total of 32,348
liver transplants were performed with 2894 in Latin America. Table 4 shows the number of liver transplants
performed as well as the number of patients on the waiting list in the LAC countries [78,79] .

Loco-regional therapy
Several minimally invasive treatment options for patients with unresectable HCC have been developed
including (1) curative therapies such as radiofrequency ablation (RFA), percutaneous ethanol injection (PEI),
microwave ablation (MWA), cryoablation (CA), irreversible electroporation (IRE), and (2) palliative
therapies such as chemoembolization transcatheter-arterial chemoembolization (TACE) or trans-arterial
radioembolization (TARE).

Curative options: liver ablation
These are ablative techniques that use chemical or thermal energy. EASL clinical practice guidelines
recommend the use of this ablative therapy in very early (single lesion < 2 cm) and early stage (2-3 nodules
< 3 cm) HCC. Ablation is recommended when resection or transplantation are not an option for HCC
[80]
patients . Tumor cell destruction can be produced through chemical substance injection (PEI) or through
temperature alteration (radiofrequency, microwave, laser or cryotherapy). Although there are several options,
[5]
RFA is the first choice .
RFA is uses an alternating electric current between 460-500 kHz which is applied to the lesion via a
radiofrequency electrode. It induces the electromagnetic field to produce an oscillation of tissue ions and
[80]
frictional heating, leading to coagulative necrosis and cell death a temperatures of 60-100 °C . RFA is more
beneficial than PEI in patients with early stage HCC. It offers 5-year-survival rates up to 76% when used as
[81]
the main therapy in patients with resectable HCC. Based on BCLC criteria , it is important to note that
[82]
results of RFA are optimal in patients with tumor > 3 cm . In Mexico, PEI and RFA are available treatment
[18]
options with successful results .
On the other hand, PEI is a good option for nodular HCC. This is the most widely used method for chemical
ablation but has the disadvantages of non-uniform diffusion and uncontrollability of injected alcohol in
large tumors. Hence, PEI is applied for the treatment of small HCC. It produces complete necrosis in 90%
of tumors < 2 cm, and in 50% of tumors measuring 3-5 cm [83,84] . The main drawback of PEI is the high
[85]
local recurrence rate, which is 43% in lesions > 3 cm . In Brazil, percutaneous ablation of early HCC is
[74]
recommended more frequently than in other LAC countries .

Regarding MWA, it was initially developed to work around the heat sink and tissue impedance limitations
of RFA in the liver. RFA and MWA have similar mechanism of inducing cell death through increasing tissue
temperature by the continuous realignment of polar molecules within a microwave field at frequencies of
[86]
915/2450 MHz . Microwaves radiate throughout all tissue without impedance, allowing a larger tissue to be
heated with each application. This technique is less invasive than hepatic resection and may be considered
for patients for whom resection may be contraindicated because of age or comorbidities such as portal
[87]
hypertension .
Other modalities of ablation currently employed in clinical practice are CA and IRE. CA destroys tissue,
causing necrosis of the tumor by freezing at temperatures between -35 °C to -20 °C using the Joule-Thomson
theory in the thawing process. This theory describes the temperature change of a gas when it is forced
[80]
through a valve while it is kept insulated so that no heat is exchanged with the environment . Tissue
destruction is carried out through two mechanisms, a direct cellular injury and a vascular related injury.
With respect to patient selection, it is necessary to consider: (1) patients with a single HCC < 5 cm in