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Page 2 of 11 Kato et al. Mini-invasive Surg 2021;5:5 I http://dx.doi.org/10.20517/2574-1225.2020.98

INTRODUCTION
[1]
On the basis of a study by Ginsberg et al. , it has been considered that lobectomy is the standard procedure
for lung cancer treatment. However, more than 20 years have passed since this evidence was reported, and
the concept may be inappropriate for small-sized lung cancers in the present era. Recently, the number of
detectable small-sized tumors has been increasing owing to the widespread use of computed tomography (CT).
It has been reported that prognosis is good if the tumor has a ground-glass opacity (GGO). In their report,
[2]
Ginsberg et al. did not adequately consider the characteristics of ground-glass nodules. Noguchi et al. reported
[1]
that wedge resection for small, non-small cell lung cancers (NSCLCs) with GGO has been associated with
favorable outcomes.

Moreover, most GGO-dominant lung nodules are adenocarcinoma in situ (AIS) or minimally invasive
[3,4]
adenocarcinoma, which has a good pathological prognosis . Therefore, the trend of surgical procedures
for small-sized GGO-dominant lung nodules has changed from lobectomy to sublobar resection. According
to the annual reports from the Japanese Association of Thoracic Surgery, the number of sublobar resections
for lung cancer during 2013 to 2017 gradually increased from 23.7% to 27% . Among sublobar resections,
[5-9]
wedge resection and anatomical sublobar resections (e.g., segmentectomy) have become widely performed
for lung cancers owing to recent technological advancements.

This article aims to describe the indications, methods, problems, and improvements of sublobar resections
for small-sized GGO-dominant lung cancers based on the recent literature. We also describe our recent
experience with sublobar resections and prospects for future procedures regarding sublobar resections for
small-sized lung cancers.

INDICATIONS FOR SUBLOBAR RESECTION
Many reports have compared the use of sublobar resection and lobectomy in small-sized lung cancers,
especially those less than 2.0 cm in diameter [10-13] . A randomized trial for peripheral small-sized lung
cancer < 2.0 cm in diameter, with or without GGO components such as CALBG 140503 and JCOG0802/
WJOG4607L, is currently in progress, and the superiority of sublobar resections is expected to be
proven [14,15] .

[16]
[3,4]
The prognosis of small-sized GGO-dominant lung cancers is generally good . Yano et al. reported that
patients with small-sized GGO-dominant lung cancers were good candidates for limited wedge resection
and segmentectomy. Among tumor characteristics seen on CT, tumor size and GGO ratio are important
factors for the indications of sublobar resection. Asamura et al. reported that tumors < 2 cm in diameter
[4]
with a GGO ratio > 75% on radiography were pathologically non-invasive. Nakata et al. [17] indicated
that patients with GGO ratios > 50% should be considered candidates for sublobar resection, although
those with a GGO ratio of 50% exhibited vessel infiltration and experienced local recurrence after wedge
[18]
resection. Recently, Sagawa et al. reported that lung cancer patients with a GGO ratio of > 80% were good
candidates for sublobar resection.

On the basis of these reports, we have indicated sublobar resection for indeterminate lung nodules in our
institution when tumor characteristics meet the following criteria, to strictly secure oncological outcomes:
(1) a tumor size < 2 cm; and (2) a GGO ratio > 80%. Moreover, sublobar resection has also been indicated
for patients whose heart and pulmonary functions are compromised to preserve pulmonary function .
[19]
In other words, sublobar resection is indicated for the following two types: (1) an intentional curative
resection for small-sized GGO-dominant lung cancer; and (2) a palliative resection for compromised
patients with whom lobectomy is intolerable due to poor pulmonary function.