Lung Cancer: Keys to Radiographic Assessment and Staging

Lung cancer is the leading cause of cancer-related deaths worldwide. Numerous treatment options are available, but deciding which modality to pursue is dependent on a detailed and accurate assessment of the disease process. Lung cancer staging is a validated tool that involves careful identification of the tumor, lymph node involvement, and metastatic spread. It is the first step in the workup of any newly diagnosed lung malignancy. This computed tomography (CT) image shows a right hilar mass invading the mediastinum (stage T4), with mediastinal lymphadenopathy (N3).

The total incidence of lung cancer in the United States has remained relatively constant over the last 20 years, despite the increase in public awareness regarding smoking cessation. A steady drop in male incidence has been mirrored by a steady increase in female incidence. Lung cancer mortality has also not decreased significantly, indicating that—despite better means of detection and surveillance—lung cancer is frequently not identified early enough to make a significant difference in survival. Data shown are per 100,000 persons and are age-adjusted to the 2000 U.S. standard population for the 10 primary sites with the highest invasive cancer incidence rates, from the Centers for Disease Control and Prevention.^[1]

Lung cancer staging relies on the TNM system designed jointly by the Union Internationale Centre le Cancer (UICC) and the American Joint Committee on Cancer (AJCC). The system is based on the spread of the primary tumor (T), the extent of lymph node involvement (N), and the presence or absence of metastases (M). The T, N, and M combination determines the appropriate stage, numbered I through IV, with subdivisions, labeled A or B. Each specific stage is associated with therapeutic and prognostic implications.

The histology slide demonstrates small cell lung cancer (SCLC). The TNM lung cancer staging system is primarily utilized for non-small cell lung cancer (NSCLC) cases, which account for approximately 75% of lung cancer diagnoses. The TNM system may be applied to small cell lung cancer, but management decisions are not as closely guided by it. Approximately 60% of patients with SCLC are metastatic upon presentation; therefore, staging is more an issue of identifying patients with localized versus metastatic disease. The methods used to identify disease distribution are the same for NSCLC and SCLC. Image courtesy of Wikipedia Commons.

This chest radiograph shows a large left midlung mass. A host of different radiographic options are available for lung cancer staging. These imaging studies are frequently used in combination with one another for best effect. Conventional chest radiography is the means by which lung cancer is often incidentally first identified. It allows for a coarse measurement of primary tumor size and may identify mediastinal lymphadenopathy. Indirect, nonspecific findings associated with a primary mass include pleural effusion, atelectasis, obstructive pneumonitis, and mediastinal widening.

This chest radiograph shows complete collapse of the left lower lobe (left), which was found to be an endobronchial tumor on CT (right). Chest radiographs may sometimes only reveal secondary signs of an underlying mass. Opacities on chest radiographs may require follow-up imaging to document resolution of either atelectasis or infection and ensure no underlying mass lesion is present.

For incidentally detected pulmonary nodules, many clinicians and radiologists follow guidelines developed by the Fleischner Society (shown),^[2] which provide evidence-based recommendations on when to repeat imaging of pulmonary nodules in order to assess growth rate and the need for tissue diagnosis. Risk factors for use of the criteria include, among others, family history; smoking history; asbestos, radon, and uranium exposure.

This CT image shows a large left lung mass extending into the hilum. After initial detection on chest radiograph or if there is high clinical suspicion, CT of the chest allows for excellent visualization of the primary tumor with the ability to accurately measure tumor size and the extent of intrathoracic invasion. The reported sensitivity and specificity for the detection of mediastinal lymph nodes are mixed, but the negative predictive value approaches 85%.

This CT image shows multiple low attenuation lesions from lung cancer metastases. Additional imaging may be directed based on localizing symptoms. CT scans are excellent for the evaluation of abdominal and pelvis disease spread. The most common sites of extrathoracic metastasis are the brain, bone, liver, and adrenal glands (in decreasing order).

This CT image shows a large left adrenal mass in a patient with lung cancer. Routine CT imaging of the abdomen and pelvis may identify indeterminate lesions that must be differentiated from benign incidental findings in order to guide treatment planning. Dedicated liver and adrenal protocol CT and magnetic resonance imaging (MRI) are available to aid in discrimination.

This MRI image shows multiple metastatic lesions in a patient with SCLC. MRI is the best means of identifying brain and spine metastases. SCLC and adenocarcinoma commonly metastasize to the brain. Not all patients with lung cancer warrant MRI imaging of the brain or spine, but those with neurologic symptoms or widespread metastatic disease may benefit.

This CT image demonstrates soft-tissue density along the pleura in a patient with mesothelioma. MRI of the chest may be needed for patients with allergies to iodinated contrast, or if there is potential involvement of the mediastinal structures which may dictate treatment planning. Unfortunately, the spatial resolution is not as precise as with CT and is limited by respiratory and cardiac motion artifacts because image acquisition time is greater.

These bone scans show metastases in the left scapula and multiple bilateral ribs. Whole-body nuclear medicine bone scanning allows for the detection of bony metastatic disease, which is usually identified by multiple asymmetric areas of increased uptake. SCLC is notorious for the presence of boney metastases, and so bone scanning is useful in both staging and follow-up imaging. It is important to rule out fractures and degenerative diseases in any patient as they may cause false-positive interpretations.

Positron emission tomography (PET, shown) is an excellent modality in lung cancer staging. It allows for a combination of functional and anatomic assessment of lesions, which is especially useful in detecting nodal involvement or metastatic spread. Tumor cells have a higher than normal metabolism, detected on PET by their increased glucose uptake, which allows one to detect the extent of metastatic disease as well as treatment response.

These CT (top left), PET/CT (top right), and PET (bottom) images show a mass in the pleural space of the right lung. With PET/CT, assessment of metabolic activity and excellent spatial resolution are both possible. PET/CT is more accurate than CT alone, PET alone, or visual correlation between PET and CT. PET/CT is becoming the standard of care for initial workup and treatment follow-up.

Endoscopic ultrasound (shown) is one method used by interventionalists that allows for real-time visualization of lymph nodes or primary tumor for sampling. The TNM classification system is used as both a pretreatment clinical classification (cTNM) and a postsurgical histopathologic pathological classification (pTNM). cTNM guides initial therapy, whereas obtaining a tissue sample for pTNM allows for adjuvant treatment and prognostic planning. Image courtesy of Wikipedia Commons.

Once lung cancer has been appropriately staged, primary and adjuvant therapeutic planning can commence. The treatment options and associated mortality for NSCLC change dramatically with each stage. For SCLC, patients with limited disease are treated with radiation; patients with extensive disease are treated with chemotherapy plus radiation, with survival rates of 10% and 3%, respectively. Surgery is not usually an option in SCLC.