and RFA have both demonstrated good clinical
efficacy and cancer control of 89% and 90%, respectively, with comparable complication rates. 22
There have been no studies performed directly
comparing the modalities.
Cryoablation
Cryoablation is performed through the insertion of a probe into the tumor, which may
be done through a surgical or percutaneous
approach. Once the probe is in place, a high-pressure gas (argon, nitrogen) is passed
through the probe and upon entering a low
pressure region the gas cools. The gas is able
to cool to temperatures as low as –185°C. The
tissue is then rewarmed through the use of helium, which conversely warms when entering
a low pressure area. The process of freezing
followed by rewarming subsequently causes cell
death/tissue destruction through direct cell
injury from cellular dehydration and vascular
injury. Clinically, 2 freeze-thaw cycles are used
to treat a tumor. 23, 24
RFA
Radiofrequency ablation, or RFA, targets tumors via an electrode placed within the mass that
produces intense frictional heat from medium-frequency alternating current (approximately
500 kHz) produced by a connected generator
that is grounded on the patient. The thermal
energy created causes coagulative necrosis. Due
to the reliance on heat for tumor destruction,
central lesions are less amenable to this approach because of the “heat sink” effect from
the hilum. 24
Microwave Ablation
Microwave ablation, like RFA, relies on the
generation of frictional heat to cause cell death
by coagulative necrosis. In this case, the fric-
tion is created through the activation of water
molecules; because of the different thermal
kinetics involved with microwave ablation, the
“heat sink” effect is minimized when treatment
is employed near large vessels, in comparison to
RFA. 24 The data on this mechanism of ablation
are still maturing, with varied outcomes thus far.
One study demonstrated outcomes comparable
to RFA and cryoablation, with cancer-specific
survival of 97.8% at 3 years. 25 However, a study
by Castle and colleagues26 demonstrated higher
recurrence rates. The overarching impediment
to widespread adoption of microwave ablation
is inconclusive data gleaned from studies with
small numbers of patients with limited follow
up. The role of this modality will need to be
revisited.
Irreversible Electroporation
Irreversible electroporation (IRE) is under
investigation. IRE is a non-thermal ablative
technique that employs rapid electrical pulses to
create pores in cell membranes, leading to cell
death. The postulated benefits of IRE include
the lack of an effect from “heat sinks” and less
collateral damage to the surrounding tissues,
when compared with the thermal modalities.
In a human phase 1 study of patients undergoing IRE prior to immediate surgical resection,
the procedure appeared feasible and safe. 27
Significant concerns for this method of ablation
possibly inducing cardiac arrhythmias, and the
resultant need for sedation with neuromuscular
blockade and associated electrocardiography
monitoring, may impede its implementation in
nonresearch settings. 24
ACTIVE SURVEILLANCE
Due to the more frequent use of imaging for
various indications, there has been an increase
in the discovery of small renal masses (SRM);
85% of RCC that present in an asymptomatic
or incidental manner are tumors under 4 cm
in diameter. 28, 29 The role of active surveillance is
evolving, but is primarily suggested for patients
who are not candidates for more aggressive
intervention based on comorbidities. A recent
prospective, nonrandomized analysis of data
from the Delayed Intervention and Surveillance
