Short Communication
Percutaneous Microwave Ablation of Small Renal Cancers: A Novel Treatment Modality
Mark Evans and Ali Thwaini*
Department of Urology, Belfast City Hospital, Belfast, UK
*Corresponding author: Ali Thwaini, Department of Urology, Belfast City Hospital, Belfast, UK
Published: 27 Sep, 2017
Cite this article as: Evans M, Thwaini A. Percutaneous
Microwave Ablation of Small Renal
Cancers: A Novel Treatment Modality.
Clin Surg. 2017; 2: 1646.
Short Communication
The diagnosis of renal cancer (RCC) is on the rise, with a clear stage shift towards an earlier
detection. Mortality rates, however, have not increased and have actually fallen in certain parts of
the world [1].
The main reason is the increase in radiological imaging, with more than 50% of RCC being
incidentally diagnosed with a resultant parallel decrease in clinical stage (70% T1) [2-4].
The current gold standard in treating early stage RCC is nephron sparing surgery as it achieves
comparable oncological outcomes to radical nephrectomy and preserves post-operative renal
function [2,5].
Focal ablative therapies constitute a viable alternative for those who are high risk surgical
candidates and those who are not keen on major operations. Most of the ablative techniques can be
performed percutaneously under local anaesthetic and are associated with a shorter length of stay.
Moreover, they have been shown to have minimal impact on post-operative renal function with
acceptable oncological outcomes [6,7].
Microwave ablation (MWA)
This novel technique in the management of small renal masses was first developed to treat liver
lesions with promising results [8]. Microwave energy causes water ion oscillation and frictional
heat much like radiofrequency ablation (RFA). However, in vivo and ex vivo models have shown
consistently higher intra-lesional temperatures attained over less time than RFA. It is less susceptible
to rising tissue impedance and the active heating may limit heat sink phenomenon [9]. This achieves
larger ablation zones and may improve the rate of treatment success.
A meta-analysis reported no significant difference between cancer specific survivals of RFA and
partial nephrectomy however selection bias and short follow up make interpretation difficult [10].
There is an increasing evidence of the efficacy and safety of the MWA for renal masses, with
reports of its superiority over RFA for energy delivery into the targeted areas, with a potential higher
rate of peri-operative complications, especially with tumours of higher complexity [11].
In an unpublished series, we compared the treatment response, oncological outcomes and the
safety profile of RFA and MWA. Of 185 patients represented in this study who underwent 215
procedures; 136 RFA and 79 MWA procedures where examined. Eight patients received MWA
following a failed treatment or local recurrence from RFA. No patients received RFA after MWA. 15
patients had repeat RFA. A further 2 patients required 3 RFA procedures. The indications for these
were 13 failed treatments, 3 local recurrences and 3 synchronous small renal masses at presentation.
3 patients received repeat MWA for treatment failure. 6 patients within the RFA cohort had 2
lesions treated simultaneously and a single patient had 3 masses ablated in a single sitting. All MWA
where performed on single lesions.
Tumour response was observed after 73 (92%) MWA and 113 (83%) RFA procedures, however
this did not reach statistical significance (p=0.09).
Multivariate analysis showed no statistically significance between tumour characteristics and
the chance of treatment failure in the RFA group; however a lesion location between the polar lines
made a unique contribution to a similar model ran for the MWA group (p=0.03).
At a median follow up was 19 months for MWA (IQR 9-26.5) and 57 months for RFA (IQR
39-78), local recurrence-free survival was 83% and 95% in successful RFA and MWA procedures
respectively, which was not statistically different (p=0.85). Overall survival was 76.1% in RFA and 99% in MWA (p=0.16). Cancer specific survival was 97% for RFA and 100% in MWA (p=0.8).
Complication rate was significantly higher in MWA (p=0.04).
Multivariate analysis of tumour characteristics did not reveal any
variable that significantly contributed to the complication rate of RFA
or MWA.
MWA, however, is still regarded as investigational but it utilises
electromagnetic energy with thermal properties that may make it
superior to RFA. As a relatively new technique there is a lack of data
but some small short term studies have shown high treatment success
and local recurrence-free survival [11,12]. To our knowledge no study
has previously compared these treatment modalities.
Our results show a higher complication rate within the MWA
group. This could be possibly due to the intrinsic thermal properties
of the MWA. Its resistance to the heat sink phenomenon and rising
tissue impedance may provide treatment advantage but also makes
spreading to affect an adjacent structure more likely if imperfectly
targeted. As this new technology develops improvements to guidance
of the probe and monitoring of the sphere expansion could reduce the
rate of complication. The operator’s awareness of this more aggressive
heating source may also help explain the relationship found between
a lesion local between the polar lines and treatment failure in MWA.
It may be that treatments where cut short due to a fear of causing
renal unit failure with a prolonged treatment in a central location.
In conclusion, MWA constitutes a viable treatment option for
small renal cancers. Our study showed high rates of local control
for both modalities, but with higher peri-operative complications
in MWA. This may improve with increasing experience and
improvements to the technology. Longer follow is required to validate
the existing results.
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