Risk Factors for SPN
Solitary pulmonary nodules should be considered potentially cancerous (malignant), until proven otherwise. Risk factors that increase the chance that an SPN is malignant include the following:
- History of cigarette smoking (some researchers include marijuana smoking as well, but the evidence is controversial)
- Age older than 45 years
- Male gender
- Presence of respiratory symptoms
- History of cancer elsewhere in the body
Factors that increase the chance that the nodule is benign include the following:
- Patient has never smoked
- Patient is younger than 35 years old
- Patient lives in an area with a high incidence of histoplasmosis or coccidioidomycosis
Risk for Chronic Infections that Can Lead to SPN
If the patient has lived in a geographical area with a high incidence of infection that can lead to SPNs, that person is at a higher risk for developing an SPN. For example, in the United States, histoplasmosis is more prevalent in the Ohio River Valley, especially Tennessee and Kentucky, than in other parts of the country. Blastomycosis is more common in the upper Midwest.
Many people who harbor fungi that can cause SPNs never actually develop an SPN or other respiratory symptoms. Patients with a weakened immune system (e.g., due to disease, or surgery) are at greater risk for developing infectious SPNs. Patients with chronic lung disease are at an increased risk for fungal infections that can cause SPNs.
Occupational Risks for SPN
Certain occupations, such as bridge building and farming, are associated with exposure to fungi that can lead to SPNs. A history of extensive asbestos exposure also has been linked to the development of malignant solitary pulmonary nodules.
Very rarely, pet owners or people who work with animals (particularly dogs) can become infected with Dirofilaria immitis, a type of worm that can lead to the development of solitary pulmonary nodules.
SPN Risk in Patients with a History of Cancer or Benign Neoplasm
In patients with a history of extrathoracic malignancy (cancer outside of the chest region) or benign neoplasms, there is a 50 to 70 percent chance that an SPN is metastatic cancer.