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
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
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.”