Pneumococcal pneumonia linked to lung cancer risk

Pneumococcal pneumonia is significantly associated with risk for lung cancer, show findings from a national study in Taiwan.

Jun-Jun Yeh (Ditmanson Medical Foundation Chia-Yi Christian Hospital, Taiwan) and colleagues used data from the country’s National Health Insurance Database to generate a cohort study including 22,034 adult patients who were diagnosed with pneumococcal pneumonia between 1997 and 2010, and 88,136 who were not.

They found that during follow-up, the incidence of lung cancer was 3.25-fold greater among the pneumococcal pneumonia cohort than in the control cohort, at 28.2 versus 8.7 cases per 1000 person–years. In regression analyses adjusting for age, gender, and comorbidity, this equated to a 4.24-fold increased risk for lung cancer over 14 years among patients with pneumococcal pneumonia.

The risk was particularly high among men, who had an 85% greater risk for developing lung cancer after pneumococcal pneumonia than women, which the authors say may be due to greater smoking incidence in men.

Additionally, older patients had the greatest risk, with those aged 75 years and over 18.7 times more likely to develop lung cancer after the infection than those aged 20 to 45 years. Writing in Lung, the team note that the findings could be due to reverse causality, with pneumonia infections a consequence of a weakened immune system due to occult lung cancer. Additionally, diagnostic investigations for pneumonia may increased the likelihood for lung cancer detection.

To account for this, they excluded lung cancer diagnosed within a year of pneumococcal pneumonia, and still found a significantly greater incidence of lung cancer compared with controls; however the incidence rate ratio was much reduced at 1.3 compared with 11.1 in patients diagnosed within a year.

The team say that theirs is the first study to explore the relationship between pneumococcal pneumonia and lung cancer incidence, adding to community- and hospital-based reports of an association between pneumonia and the disease.

“Our findings provide epidemiological evidence that pneumococcal pneumonia is a risk factor for subsequent lung cancer and that pneumococcal pneumonia patients should be monitored carefully for lung cancer development,” the authors conclude.

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