Thoracic Imaging 2003 - Society of Thoracic Radiology

WEDNESDAY
224
Lung Cancer Staging
Ann N. Leung, M.D.
Objective: To review the international (TNM) system for staging
lung cancer with emphasis on identification of nonresectable
disease.
INTERNATIONAL SYSTEM FOR STAGING LUNG
CANCER
In patients with non-small cell lung cancer, staging is performed
for both prognostic and therapeutic purposes. The international
system enables a consistent and reproducible description
of the extent of tumor by use of three anatomic descriptors:
T, N, and M (1). T refers to the status of the primary tumor with
numerical suffixes ranging from 1 – 4 which describe increasing
size or extent. N refers to the status of the regional lymph nodes
with suffixes ranging from 0 – 3 which describe increasing
extent; M refers to the status of metastatic involvement with suffixes
0 and 1 which describe its absence or presence, respectively.
Overall stage of disease is then derived from grouping of
TNM subsets, which share similar prognosis and treatment
options.
CT AND MR ASSESSMENT OF TNM DESCRIPTORS
Assessment of the T descriptor requires determination of the
size and anatomic extent of tumor and its relation to a number
of intrathoracic structures. In the TNM system, T4 or unresectable
primary tumors invade the mediastinum, heart, great
vessels, trachea, esophagus, vertebral body, or carina; or are
associated with a malignant pleural or pericardial effusion; or
are associated with a satellite tumor nodule or nodules within
the ipsilateral primary tumor lobe. CT and MR are roughly
equivalent in their accuracy of T staging in patients with lung
cancer (2); MR has been show to be slightly superior in the
assessment of chest wall invasion and mediastinal invasion and
in determining the superior extent of Pancoast tumors (2-4).
Assessment of the N descriptor requires determination of the
extent of regional lymph node involvement. In the regional
lymph node classification system (5) adopted by the American
Joint Committee on Cancer in 1997, 14 numbered stations are
used to designate the status of mediastinal, hilar, and intrapulmonary
nodes. In the TNM system, N3 or unresectable nodal
disease consists of metastasis to contralateral mediastinal, contralateral
hilar, ipsilateral or contralateral scalene, or supraclavicular
nodes. CT and MR have been shown to be roughly equivalent
in their accuracy of N staging in patients with lung cancer
(2, 6). Using 1 cm short axis diameter as the size criterion for a
pathologically enlarged node, sensitivity and specificity of CT
for nodal metastases have been reported to range from 61-64%
and 62-93%, respectively (7,8).
Distant metastases in a patient with non-small cell lung is
classified as M1, unresectable disease. Traditionally, the standard
evaluation for detection of metastatic disease has consisted
of a history and physical, hematologic survey, liver enzyme
analysis, and CT of the chest and upper abdomen. In the
absence of clinical signs and symptoms or laboratory and radiologic
abnormalities, the patients have been presumed to be free
of distant disease.
PET STAGING OF LUNG CANCER
Staging of lung cancer with whole-body PET imaging is an
accurate method to distinguish between patients with resectable
versus nonresectable disease (9). In comparison to cross-sectional
modalities, PET has both significantly higher sensitivity
(range, 83 – 93%) and specificity (range, 82 – 99%) in identifying
nodal involvement (N status). Whole-body PET imaging
also permits detection of distant metastases without any further
increase in radiation exposure to patients. This ability to detect
both local and distant metastatic disease has been shown to significantly
alter management in up to 37% of evaluated patients
presenting with non-small cell lung cancer (10).
Marom et al (9) compared the accuracy of whole-body PET
to conventional imaging (thoracic CT, bone scintigraphy, and
brain CT or MR) for detection of extrathoracic metastases, PET
was shown to be superior for identification of metastases involving
the bone, adrenals, and liver. However, because of normally
high levels of glucose uptake in the brain, PET had lower sensitivity
than CT or MR for detection of metastases to the brain.
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