Childhood Pneumonia May Be Associated With Cancer Risk

Children who are hospitalized for pneumonia have a higher incidence of developing common pediatric cancers, according to a large Danish study published in BMJ.

The researchers, from Aarhus University Hospital in Denmark, used national health registries to observe the incidence of leukemia, lymphoma and brain cancer — the three most common cancers for children – in 83,935 patients who were hospitalized with a pneumonia diagnosis compared to the general population. They then calculated standardized incidence ratios (SIRs) as the measure of relative risk.

The researchers found a total of 168 cancer diagnoses. Substantially increased risks for lymphoid leukemia, myeloid leukemia, Hodgkin’s lymphoma, non-Hodgkin’s lymphoma and brain cancer were seen during the first six months after pneumonia-related hospitalizations. Regarding short-term incidence, many of these risks decreased, except for non-Hodgkin’s lymphoma and brain cancer, where the risk persisted beyond five years.

SIRs appeared higher in girls and in children diagnosed with immunodeficiencies or congenital malformations, and two-fold higher in children up to age 14.

While causes for pneumonia were varied — including bacteria (14 percent), virus (22 percent) and unspecified (64 percent) – the majority of children did not have immune deficiencies recorded at the time of their pneumonia diagnosis.

However, this is not to say that the immune system did not play a role in the eventual cancer diagnosis. The more children tended to visit the hospital — meaning that pneumonia may not have been the first clinical disease for some of them – the chance they would develop cancer was higher.

“We speculate if the associations demonstrated may be due to cancer-related impairment of the immune system, making a child more vulnerable to severe infections such as pneumonia,” the authors wrote. “In children with aggressive typesx of cancer, the infection may lead on to a cancer diagnosis, whereas in children with a more indolent cancer, the infection occurs in the preclinical phase.

Another explanation behind the finding is that when children come in and end up being diagnosed with pneumonia, they usually undergo chest X-rays and blood tests. Any suspicious findings can lead to further testing and, ultimately, a cancer diagnosis. Also, lymphoma with mediastinal masses or with lung involvement might have initially been diagnosed incorrectly as pneumonia in some patients.

Since the exact cause of the correlation between childhood pneumonia diagnoses and cancer risk is still unknown, the findings from this study warrant further investigation, the researchers said.