Thoracic Imaging 2003 - Society of Thoracic Radiology

WEDNESDAY
216
Small T1 Lung Cancer: Imaging and Its Prognostic
Implication
Kyung Soo Lee, M.D.
Department of Radiology, Samsung Medical Center,
Sungkyunkwan University School of Medicine, Seoul, Korea
Introduction
Patients with peripheral lung cancer less than 3 cm in diameter
(T1 lung cancer) without nodal or distant metastasis, designated
as stage IA (T1N0M0) in the TNM staging system, have a
greater than 50% 5-year postoperative survival rate. Although
initial studies suggested a low prevalence of nodal metastases in
T1 lung cancer, several recent studies have reported relatively
high frequency of mediastinal lymph node metastases. Seely et
al (1) reviewed the CT scans and surgical findings in 104
patients with T1 lesions, and found that 21% of patients had
nodal metastases as proved by complete nodal sampling using
either mediastinoscopy or thoracotomy. The reported frequency
of extrathoracic metastases in T1 lung cancer differs widely (0-
24%), because of lack of uniformity in patient selection as well
as methods of assessing the presence of metastases. Recently
Jung et al (2) saw 13% of patients with T1 lung cancer had
extrathoracic metastases at the time of diagnosis and additional
11% of patients (total 24% of patients) had metastases at oneyear
follow-up study.
Because small T1 peripheral lung cancers show sizable frequency
of mediastinal nodal or extrathoracic metastasis, it is
important to know on imaging studies which tumor will have
mediastinal nodal or extrathoracic metastasis. In this lecture, the
author will focus on imaging (CT and 18 F-luorodeoxyglucose
positron emission tomography: FDG-PET) findings of small
peripheral lung cancer correlated with prognostic implications.
CT Findings of Small Peripheral Adenocarcinoma of the
Lung and Prognostic Implication
Adenocarcinoma of the lung is the commonest histopathologic
type of lung cancer and its incidence is reported to
increase. In addition, it is reported that screening with low-dose
CT can improve the detection of lung cancer, especially adenocarcinoma,
at an earlier and potentially more curable stage.
Because adenocarcinoma of the lung comprises histopathologically
of heterogeneous group of tumors, it is difficult to predict
a prognosis in patients with surgically resectable peripheral adenocarcinoma
of the lung (3). However, in recent several studies,
it was suggested that the extent of bronchioloalveolar carcinoma
component in a small peripheral adenocarcinoma reflects clinicopathologic
and prognostic characteristics of the tumor. As the
component of bronchioloalveolar carcinoma within a tumor
increases in extent, the adenocarcinoma shows better prognosis.
Furthermore, pure bronchioloalveolar carcinoma without central
fibrosis shows better prognosis than that with fibrosis (4).
Localized bronchioloalveolar carcinoma may appear as an
area of GGO, as a mixed area of GGO and more dense consolidation,
or as a nodule (5,6). Kuriyama et al (7) suggested that
the percentage of GGO in a localized bronchioloalveolar carcinoma
is larger than that in other adenocarcinomas. Aoki et al (8)
asserted that adenocarcinoma appearing as localized GGO
shows slow growth. In addition, Jung et al (2) suggested that the
prevalence of extrathoracic metastasis is significantly lower in a
small peripheral lung cancer with GGO than without it.
Kim et al (9) correlated the high-resolution CT findings of
peripheral small adenocarcinoma of the lung in 224 patients
with histopathologic subtypes and evaluated whether there are
any CT findings that help to predict a prognosis of the tumor.
One hundred and thirty-two patients had bronchioloalveolar carcinoma
and 92 had adenocarcinoma. The extent of GGO was
greater in bronchioloalveolar carcinomas (29% + 31.6, mean +
standard deviation) than in other adenocarcinomas (8% + 13.3)
(p < .001). The extent of GGO was significantly greater in
patients without recurrence (p = .020), nodal (p = .017), and distant
(p = .007) metastases than in patients with them. They concluded
that the extent of GGO within a nodule is greater in
bronchioloalveolar carcinomas than in other adenocarcinomas.
Greater extent of GGO also correlates with improved prognosis.
Similarly Aoki et al (10) evaluated the prognostic importance
of high-resolution CT findings of peripheral lung adenocarcinoma.
The marginal characteristics of nodules and extent of GGO
within the nodules at preoperative high-resolution CT were analyzed
retrospectively. Regional lymph node metastasis and vessel
invasion were histologically examined in surgical specimens.
Survival curves were calculated according to the Kaplan-Meier
method. The frequency of lymph node metastasis (4% [1 of 24])
and vessel invasion (13% [three of 24]) in adenocarcinomas
with GGO components of more than 50% were significantly
lower than those with GGO components of less than 10%
(lymph node metastasis, p < .05; vessel invasion, p < .01). The
patients with GGO components of more than 50% showed a significantly
better prognosis than those with GGO components
less than 50% (p < .05). All 17 adenocarcinomas smaller than 2
cm with GGO components of more than 50% were free of
lymph node metastasis and vessel invasion, and all these
patients are alive without recurrence. Coarse spiculation and
thickening of bronchovascular bundles around the tumors were
observed more frequently in tumors with lymph node metastasis
or vessel invasion than in those without lymph node metastasis
or vessel invasion (p < .01). They concluded that high-resolution
CT findings of peripheral lung adenocarcinomas correlate well
with histologic prognostic factors.
Focal GGO has been detected increasingly by low-dose helical
CT in lung cancer screening. Although focal GGO suggests
in situ neoplastic lesion in the peripheral lung, it remains controversial
how to manage these lesions. Nakata et al (11) evaluated
the pathologic and radiologic characteristics of focal GGO.
Forty-three patients with persistent (mean of 3.7 months) focal
GGO < 2 cm in diameter were studied. The histologic diagnoses
were bronchioloalveolar carcinoma in 23 patients, adenocarcinoma
with mixed subtypes in 11 patients, and atypical adenomatous
hyperplasia (AAH) in nine patients. None of 34 patients
with carcinoma had lymph node metastasis. GGO with solid
components on CT were highly associated with adenocarcinoma
(malignant rate, 93%). They concluded that focal GGO after
observation for several months is a finding of early adenocarcinoma
or its precursors. Especially lesions > 1 cm in diameter or
GGO with solid components are significant signs of malignancy.
In a study to determine the relationship between tumor size
and survival in patients with stage IA non-small cell carcinoma,