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Kato et al. Hepatoma Res 2021;7:10 I http://dx.doi.org/10.20517/2394-5079.2020.129 Page 13 of 15

(ConMed). In these cases, grave CO gas embolism with significant hypotension was observed, even with
2
minor HV injuries; this sometimes occurred without significant gas embolism during LLR or even RLR
using a conventional pneumoperitoneal machine. Furthermore, no systemic complications occurred after
discontinuing the use of the AirSeal system (ConMed). These findings and the mechanical actions of the
AirSeal system (ConMed) collectively imply that we should avoid using this system, particularly during
AR, where the major HVs are routinely exposed during parenchymal dissection. The AirSeal system-
related severe complications are not limited to RLR. In fact, we experienced CO embolism in a case of AR
2
exposing a major HV during LLR. On the other hand, the rates of surgical-site complications were very
low (1.8% for 57 RLR and 0% for 23 AR cases). These promising results suggest the potential advantages
of robotics, such as topical technical safety, particularly for AR; however, a comparison of surgical-site
complication rates among open, laparoscopic, and robotic AR using similar techniques [15,16] is warranted.

Previous studies compared the short-term results of RLR and LLR for HCC [20,21] . They reported that
operative time, blood loss, complication rate, and length of hospital stay were similar using the two
approaches. The authors also suggested that RLR may offer advantages over LLR in major AR procedures or
when tumors are in difficult locations, such as posterosuperior segments [20,21] . Further studies are necessary
to determine the advantages and disadvantages of RLR compared to LLR for HCC. Moreover, comparative
studies of robotic and laparoscopic AR for HCC are warranted to clarify the real significance of robotic AR
for this disease entity.

The long-term results showed that the OS rate of our 46 HCC patients who underwent RLR seemed
acceptable compared to that reported by previous studies [20,23] . Moreover, the respective OS and DFS rates of
the AR and NAR groups seemed acceptable, and the outcomes of both groups were similar. Larger studies
are needed to further define the oncologic effects of RLR or robotic AR on the treatment of HCC.

There are several difficulty scoring systems used in LLR [24,25] . We have not used these systems for assessing
the difficulty in RLR cases. We think that these systems may be also useful for RLR, but additional factors
may be considered such as the resection types requiring the curved resection plane in the absence of
ultrasonic aspirator, port placement to reduce robotic arm interference and patient body position to
facilitate optimal arm movement. Regarding the learning curve for RLR, we consider that the curve may be
more low-gradient in RLR than in LLR, if the robotic beginner has already significant experience with LLR.
However, AR is still more difficult in RLR than in LLR because of inadequate instruments for parenchymal
dissection for RLR, though the hilar dissection and vascular control and hemostasis are easier in RLR than
in LLR.

There have been no reported randomized control studies comparing RLR and LLR. At our institution,
indication of surgery and procedures are similar between the two approaches. However, both the economic
issue as a result of no insurance coverage on RLR and the issue of machine availability in the hospital
preclude randomized studies. Propensity-score matched studies and future randomized studies are
warranted.

There are limitations in this study. First, this is a retrospective study with a small sample size. Second, as
stated above, the economic issue resulting from no insurance coverage on RLR greatly affected selection of
approaches.

In conclusion, RLR may be a safe and feasible form of hepatectomy for HCC. Robotic AR for HCC can
be technically standardized with acceptable safety by the GPA and HV root-at first one-way resection.
However, further experience and comparative studies of RLR, LLR, and open resection are necessary to
define the significance of robotic AR for the treatment of HCC.