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Thoracic Imaging 2003 - Society of Thoracic Radiology

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WEDNESDAY<br />

224<br />

Lung Cancer Staging<br />

Ann N. Leung, M.D.<br />

Objective: To review the international (TNM) system for staging<br />

lung cancer with emphasis on identification <strong>of</strong> nonresectable<br />

disease.<br />

INTERNATIONAL SYSTEM FOR STAGING LUNG<br />

CANCER<br />

In patients with non-small cell lung cancer, staging is performed<br />

for both prognostic and therapeutic purposes. The international<br />

system enables a consistent and reproducible description<br />

<strong>of</strong> the extent <strong>of</strong> tumor by use <strong>of</strong> three anatomic descriptors:<br />

T, N, and M (1). T refers to the status <strong>of</strong> the primary tumor with<br />

numerical suffixes ranging from 1 – 4 which describe increasing<br />

size or extent. N refers to the status <strong>of</strong> the regional lymph nodes<br />

with suffixes ranging from 0 – 3 which describe increasing<br />

extent; M refers to the status <strong>of</strong> metastatic involvement with suffixes<br />

0 and 1 which describe its absence or presence, respectively.<br />

Overall stage <strong>of</strong> disease is then derived from grouping <strong>of</strong><br />

TNM subsets, which share similar prognosis and treatment<br />

options.<br />

CT AND MR ASSESSMENT OF TNM DESCRIPTORS<br />

Assessment <strong>of</strong> the T descriptor requires determination <strong>of</strong> the<br />

size and anatomic extent <strong>of</strong> tumor and its relation to a number<br />

<strong>of</strong> intrathoracic structures. In the TNM system, T4 or unresectable<br />

primary tumors invade the mediastinum, heart, great<br />

vessels, trachea, esophagus, vertebral body, or carina; or are<br />

associated with a malignant pleural or pericardial effusion; or<br />

are associated with a satellite tumor nodule or nodules within<br />

the ipsilateral primary tumor lobe. CT and MR are roughly<br />

equivalent in their accuracy <strong>of</strong> T staging in patients with lung<br />

cancer (2); MR has been show to be slightly superior in the<br />

assessment <strong>of</strong> chest wall invasion and mediastinal invasion and<br />

in determining the superior extent <strong>of</strong> Pancoast tumors (2-4).<br />

Assessment <strong>of</strong> the N descriptor requires determination <strong>of</strong> the<br />

extent <strong>of</strong> regional lymph node involvement. In the regional<br />

lymph node classification system (5) adopted by the American<br />

Joint Committee on Cancer in 1997, 14 numbered stations are<br />

used to designate the status <strong>of</strong> mediastinal, hilar, and intrapulmonary<br />

nodes. In the TNM system, N3 or unresectable nodal<br />

disease consists <strong>of</strong> metastasis to contralateral mediastinal, contralateral<br />

hilar, ipsilateral or contralateral scalene, or supraclavicular<br />

nodes. CT and MR have been shown to be roughly equivalent<br />

in their accuracy <strong>of</strong> N staging in patients with lung cancer<br />

(2, 6). Using 1 cm short axis diameter as the size criterion for a<br />

pathologically enlarged node, sensitivity and specificity <strong>of</strong> CT<br />

for nodal metastases have been reported to range from 61-64%<br />

and 62-93%, respectively (7,8).<br />

Distant metastases in a patient with non-small cell lung is<br />

classified as M1, unresectable disease. Traditionally, the standard<br />

evaluation for detection <strong>of</strong> metastatic disease has consisted<br />

<strong>of</strong> a history and physical, hematologic survey, liver enzyme<br />

analysis, and CT <strong>of</strong> the chest and upper abdomen. In the<br />

absence <strong>of</strong> clinical signs and symptoms or laboratory and radiologic<br />

abnormalities, the patients have been presumed to be free<br />

<strong>of</strong> distant disease.<br />

PET STAGING OF LUNG CANCER<br />

Staging <strong>of</strong> lung cancer with whole-body PET imaging is an<br />

accurate method to distinguish between patients with resectable<br />

versus nonresectable disease (9). In comparison to cross-sectional<br />

modalities, PET has both significantly higher sensitivity<br />

(range, 83 – 93%) and specificity (range, 82 – 99%) in identifying<br />

nodal involvement (N status). Whole-body PET imaging<br />

also permits detection <strong>of</strong> distant metastases without any further<br />

increase in radiation exposure to patients. This ability to detect<br />

both local and distant metastatic disease has been shown to significantly<br />

alter management in up to 37% <strong>of</strong> evaluated patients<br />

presenting with non-small cell lung cancer (10).<br />

Marom et al (9) compared the accuracy <strong>of</strong> whole-body PET<br />

to conventional imaging (thoracic CT, bone scintigraphy, and<br />

brain CT or MR) for detection <strong>of</strong> extrathoracic metastases, PET<br />

was shown to be superior for identification <strong>of</strong> metastases involving<br />

the bone, adrenals, and liver. However, because <strong>of</strong> normally<br />

high levels <strong>of</strong> glucose uptake in the brain, PET had lower sensitivity<br />

than CT or MR for detection <strong>of</strong> metastases to the brain.<br />

REFERENCES:<br />

1. Mountain CF. Revisions in the International System for Staging<br />

Cancer. Chest 1997; 111: 1710-1717.<br />

2. Webb WR, Gatsonis C, Zerhouni EA, et al. CT and MR imaging<br />

in staging non-small cell bronchogenic carcinoma: report <strong>of</strong><br />

the Radiologic Diagnostic Oncology Group. <strong>Radiology</strong> 1991;<br />

178:705-713.<br />

3. Musset D, Grenier P, Carrette MR, et al. Primary lung cancer<br />

staging: prospective comparative study <strong>of</strong> MR imaging with<br />

CT. <strong>Radiology</strong> 1986; 160:607-611.<br />

4. Heelan RT, Demas BE, Caravelli JF, et al. Superior sulcus<br />

tumors: CT and MR imaging. <strong>Radiology</strong> 1989; 170: 637-641.<br />

5. Mountain CF, Dresler CM. Regional lymph node classification<br />

for lung cancer staging. Chest 1997; 111:1718-1723.<br />

6. Martini N, Hellan R, Westcott J, et al. Comparative merits <strong>of</strong><br />

conventional, computed tomographic, and magnetic resonance<br />

imaging in assessing mediastinal involvement in surgically<br />

confirmed lung cancer. J Thorac Cardiovasc Surg 1985;<br />

90:639-648.<br />

7. Staples CA, Muller NL, Miller RR, Evans KG, Nelems B.<br />

Mediastinal nodes in bronchogenic carcinoma: comparison<br />

between CT and mediastinoscopy. <strong>Radiology</strong> 1988; 167:367-<br />

372.<br />

8. McLoud TC, Bourgouin PM, Greenberg RW, et al.<br />

Bronchogenic carcinoma: analysis <strong>of</strong> staging in the mediastinum<br />

with CT by correlative lymph node mapping and sampling.<br />

<strong>Radiology</strong> 1992; 182:319-323.<br />

9. Marom EM, McAdams HP, Erasmus JJ, et al. Staging nonsmall<br />

cell lung cancer with whole-body PET. <strong>Radiology</strong><br />

1999;212:803-809.<br />

10. Saunders CAB, Dussek JE, O’Doherty MJ, Maisey MN.<br />

Evaluation <strong>of</strong> fluorine-18-fluorodeoxyglucose whole body<br />

positron emission tomography imaging in the staging <strong>of</strong> lung<br />

cancer. Ann Thorac Surg 1999;67:790-797.

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