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Page 8 of 10 Zhao et al. Mini-invasive Surg 2018;2:26 I http://dx.doi.org/10.20517/2574-1225.2018.27

Table 3. Local tumour response to ablation and survival status at follow-up
Survival status
Local response Total
Alive Dead
Complete ablation 7 3 10
Local progression 1 1 2
No imaging follow-up 0 1 1
Total 8 5 13

While surgery is the treatment of choice in early stage NSCLC, many patients are not candidates for sur-
[1]
gery due to comorbidities . Percutaneous thermal ablation is a minimally invasive alternative treatment
[20]
option with minimal impact on the uninvolved lung parenchyma and overall pulmonary function . Our
results demonstrate that even after failed initial attempt(s) at ablation, repeat ablation can achieve local
control. Only 2 of our patients experienced local progression on follow-up imaging after repeat ablation.
Two-year overall survival in our NSCLC patients after repeat ablation was 100%. Yang et al. recently re-
[7]
ported repeat MWA to be a safe and effective treatment for local progression of medically inoperable stage
1 NSCLC after initial MWA, with 21 of 24 (87.5%) patients achieving local control after repeat MWA, and
with median overall survival 41.5 months after first MWA, similar to those treated with single MWA and
with no local progression (median overall survival 48 months) at their institution. Our results support
these findings that repeat thermal ablation is a safe and effective treatment for local progression of stage 1
NSCLC after initial ablation.

Thermal ablation may also be used for local control of secondary lung metastases. The goal in such patients
is to improve patient quality of life and prolong survival. In a series of 566 patients with 1037 lung metas-
tases of various primary origin, RFA treatment resulted in a median overall survival of 62 months, and a
[9]
4-year local control rate of 44.1%, with patients re-treated with RFA safely up to four times . Our small
sample of metastatic colorectal cancer patients re-treated with MWA all achieved local control and were
alive after a median follow-up time of 23 months. The minimally invasive nature and repeatability of abla-
tion are of utility in local control of lung metastases.

Six out of 12 patients had nodal or distant metastasis on follow-up imaging, with 2 of these patients dem-
onstrating local progression at the ablation site, suggesting systemic disease progression despite local con-
trol in the other four patients. We believe offering repeat ablation for local control is still of value, as it is
a minimally invasive technique which may improve patient quality of life and prolong survival, without
significant increase in morbidity.

In this study, we defined local tumour response to ablation as based on increase, stability or decrease in
[9]
size of ablation zone on CT . FDG-PET scan findings are more difficult to interpret, as local uptake may
be due to post-treatment inflammatory changes rather than local tumour progression, and this effect may
last up to 12 months after ablation [21-23] . Additionally, false positive FDG-PET scans have been reported
[23]
greater than 12 months after ablation . The optimal timing of FDG-PET scan after ablation is controver-
[24]
sial and not yet defined . FDG-PET is likely a useful adjunct to CT in assessing local response to ablation,
as well as for diagnosis of nodal or distant metastasis. However, further research is needed in imaging cri-
teria to determine treatment response to ablation.

This study was limited by small sample size, heterogeneity of tumour size and histology, difference of
ablation systems used and retrospective assessment. Additionally, as some patients had to travel long dis-
tances for their procedure and were not followed up by the respective teams they had been admitted under
for their ablations, follow-up CT and FDG-PET scans were occasionally not performed at the requested
time, although local tumour response to ablation was still able to be determined based on the most recent
follow-up CT. Furthermore, some patients who had nodal or distant metastasis on follow-up imaging sub-
sequently had chemotherapy, which may have influenced local response to ablation. In the future, larger