Recurrent pneumonia increases lung cancer risk for patients with AIDS

Recurrent bacterial pneumonia is associated with an increased risk of lung cancer in patients with AIDS, US investigators report in the online edition of the Journal of Acquired Immune Deficiency Syndromes. The association between pneumonia and lung cancer was especially strong amongst patients below 50.

The investigators believe that recurrent pneumonia could be causing inflammation, which in turn increases the risk of lung cancer.

Amongst people with AIDS in the US, lung cancer is the third most common cancer. Cigarette smoking has been identified as the only factor significantly associated with lung cancer risk for people with HIV in a number of studies. However, a team of US investigators found that even after adjusting for cigarette smoking, lung cancer risk was still elevated amongst people with HIV.

People with HIV, especially if they have a weak immune system, are more likely to develop serious lung disease. Three types of pulmonary disease are classified as AIDS-defining: PCP pneumonia; tuberculosis (TB); and recurrent bacterial pneumonia.

Investigators hypothesised that individuals with AIDS who developed these diseases would be at increased risk of lung cancer, because of the inflammation that they cause in the lungs.

They therefore looked at the records of 322,675 individuals who were diagnosed with AIDS between 1977 and 2002 and linked these to cancer registries. They monitored the patients’ risk of lung cancer in the ten years after their diagnosis with AIDS.

Recurrent pneumonia represented 2% of all AIDS diagnoses, the figures for TB and PCP being 4% and 26% respectively.

There was no change in the incidence of bacterial pneumonia, but the incidence of TB fell after the introduction of effective HIV therapy in 1996.

In more than ten years of follow-up, there were 853 cases of lung cancer (83 cases per 100,000 person years).

Individuals with recurrent pneumonia had a significantly higher risk of lung cancer than patients without this disease (hazard ratio, 1.63; 95% CI = 1.08 to 2.46, p = 0.02).

Of note, patients with recurrent pneumonia had a significantly increased risk of lung cancer five to ten years after their first diagnosis (p = 0.04).

Recurrent pneumonia was associated with an increased risk of lung cancer for patients aged under 50 (HR = 1.99; 95% CI, 1.26 – 3.16; p = 0.003), but not for the over 50s.

The association between bacterial pneumonia and lung cancer risk did not vary significantly in the eras before and after effective HIV therapy was introduced.

Overall, lung cancer was not linked to TB. However, the investigators did note a significantly increased risk of lung cancer for TB patients in the first year after their diagnosis with this infection. They believe that this was probably because chest x-rays diagnosed disease which was already present, or because lung cancer activated latent TB.

The investigators did not have information about the patients’ smoking habits. However, on the basis of other research involving individuals with HIV, they assumed a smoking prevalence of at least 70% amongst the patients with recurrent pneumonia.

This weakened the association between recurrent pneumonia and lung cancer to the point where it ceased to be statistically significant (70% prevalence, HR = 1.42; 95% CI, 0.93-2.14).

Nevertheless, the investigators comment: “We found that individuals with recurrent pneumonia had a significantly increased risk of lung cancer…our current observation that recurrent pneumonia was associated with increased lung cancer risk among younger, but not older PWA supports the conclusion that pulmonary infections might explain the high lung cancer risk among young PWA.”