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Catching pneumonia is a surprising way to prevent lung cancer, according to a study from the National Cancer Institute. Respiratory tract infections are generally thought to promote lung cancer through changes to the airway. Jill Koshiol and colleagues performed a study to see how pneumonia affects lung cancer risk. In contrast to chronic inflammatory respiratory conditions, pneumonia was associated with reduced cancer risk.
Data were taken from the Environment And Genetics in Lung cancer Etiology (EAGLE) case control study. A total of 2,100 patients with lung cancer and 2,120 demographically matched patients were selected. Information on history of pneumonia and tuberculosis was collected by personal interviews.
The authors speculated that individuals diagnosed with tuberculosis at a young age may avoid lung cancer risk factors such as smoking. The median age at tuberculosis diagnosis was 22. The results of the study showed no association between tuberculosis and lung cancer. For 90 percent of the subjects, the tuberculosis diagnosis occurred at least 20 years before the study began.
“Reported associations between tuberculosis and lung cancer have been inconsistent,” Koshiol noted. She suggested that the long time period between tuberculosis and study participation may have obscured any effects of the infection.
Pneumonia was different. Individuals with a history of pneumonia diagnosis had a lower rate of lung cancer, and this was especially significant for those with three or more diagnoses.
Koshiol offered possible explanations for this association:
1. Individuals who develop pneumonia may have genetic differences in immune function.
2. Antibiotic treatment may eliminate infections that increase lung cancer risk.
3. Pneumonia may stimulate the immune system to better detect and destroy cancer cells.
Koshiol concluded, “The apparent protective effect of pneumonia among individuals with multiple pneumonia diagnoses may reflect an underlying difference in immune response and requires further investigation and confirmation.”