Excerpt from Solitary Pulmonary Nodule

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Background

Patients with solitary pulmonary nodules (SPNs) are usually asymptomatic; however, SPNs pose a challenge to both physicians and patients. Whether detected serendipitously or during a routine investigation, a nodule on a chest radiograph raises several questions: Is the nodule benign or malignant? Should it be investigated or observed? Should it be surgically resected?

Most SPNs are benign, but they may represent an early stage of lung cancer. Lung cancer is the leading cause of cancer death in the United States, accounting for more deaths annually than breast, colon, and prostate cancers combined. Lung cancer survival rates remain dismally low at 14% at 5 years. Early lung cancer, when the primary tumor is less than 3 cm in diameter (stage 1A), may lead to 5-year survival rates of 70-80%. Therefore, prompt diagnosis and management of early lung cancer manifesting as SPN may be the only chance for cure.

Pathophysiology

An SPN is defined as a single, discrete pulmonary opacity that is less than 3 cm in diameter, surrounded by normal lung tissue, and not associated with adenopathy or atelectasis.

Generally, a pulmonary nodule must reach 1 cm in diameter before it can be identified on a chest radiograph. For a malignant nodule to reach this size, approximately 30 doublings would have occurred. The average doubling time for a tumor is 120 days (range, 7-590 d). A lesion at this growth rate may be present for 10 years before discovery.

An SPN may be secondary to one of the numerous differential diagnoses listed in Causes. However, more than 95% are neoplasms (most likely primary), granulomas (most likely infectious), or benign lesions (most likely hamartoma).

Frequency

United States

SPNs are one of the most common thoracic radiographic abnormalities. Approximately 150,000 cases are detected each year as an incidental finding, either on images from chest radiographs or images from thoracic CT scans (Lillington, 1991). Approximately 40-50% of these nodules are malignant. Most are bronchogenic carcinoma, but 10-30% may be solitary metastases.

Mortality/Morbidity

Most SPNs are benign, but they may represent an early stage of lung cancer.

• While lung cancer survival rates remain dismally low at 14% at 5 years, early lung cancer, ie, diagnosed when the primary tumor has a diameter smaller than 3 cm (stage 1A), can be associated with a 5-year survival rate of 70-80%.
• Accordingly, the only chance for cure of early lung cancer manifesting as SPN is prompt diagnosis and management.

Age

Risk of malignancy increases with age.

• For individuals younger than 39 years, the risk is 3%.
• The risk increases to 15% for individuals aged 40-49 years, to 43% for persons aged 50-59 years, and to more than 50% for persons older than 60 years.

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