New study links common infections with specific cancers
Liz Meszaros, MDLinx | April 27, 2020
When it comes to strange but somehow-not-surprising associations, the link between infections and cancer may take top honors. In a recent study, published in Cancer Immunology Research, researchers found that, in the years before a diagnosis of malignant cancer, patients may experience a greater number of infections. Not only that, but certain infections—influenza, pneumonia, hepatitis, and gastroenteritis—may have stronger associations with specific cancer types.
Oddly enough, most infections that affected a specific organ, with the exception of hepatitis, did not correlate with an increased risk of cancer in the same organ.
What’s behind the infection-cancer link?
“Cancer can develop in an inflammatory environment caused by infections, immunity disruption, exposure to chemical carcinogens, or chronic or genetic conditions. An individual’s immunity is thought to be a factor in the development of cancer, but additional research is needed to understand the relationship among precancerous immunity, infections, and cancer development. This information may contribute to efforts to prevent or detect cancer,” according to lead author of the current study Shinako Inaida, PhD, visiting researcher, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
Several viruses have been associated with cancer in humans, according to the American Cancer Society. Consider that human papillomaviruses has been linked to cervical and other cancers; Epstein-Barr virus can increase the risks of nasopharyngeal cancer; hepatitis B and C viruses both increase the risk of liver cancer; HIV has been linked to Kaposi sarcoma, non-Hodgkin lymphoma, and cervical cancer; and human herpes virus 8 to Kaposi sarcoma.
Infections and solid tumors
Yet, while the link between infections and non-solid tumors such as lymphoma, chronic lymphocytic leukemia, and myeloma has been previously studied, their associations to the development of solid tumors has not been.
To this end, Dr. Inaida and Shigeo Matsuno, PhD, Biomedical Science Association, Tokyo, Japan, conducted a retrospective, case-control study in 2,354 participants with malignant cancers identified in a Japanese medical claims database. The most common cancers prevalent in the study group were digestive and gastrointestinal, head and neck, and stomach cancers. Also enrolled were 48,395 controls not diagnosed with any cancers. All participants were aged 30 years or older, with no recorded immunodeficiencies.
They found that participants with cancer had higher infection rates in the 6 years before cancer diagnoses compared with controls, and with each year, the age-adjusted odds of infection increased. During the first year, those who developed cancer had a 16% higher risk of infection compared with controls. By year 6, this had increased to a 55% greater risk. The group did not investigate whether increased infection was directly linked to later cancer development. More research is needed to determine this link.
Interestingly, the greatest differences in the incidence of infections between the two groups occurred in the sixth year, or just 1 year before a cancer diagnosis. This suggests that the greatest change in immunity may occur immediately before a cancer diagnosis. In this year alone, the rate of influenza in participants diagnosed with cancer was 18% higher than in the control group, rates of gastroenteritis were 46.1% higher, rates of hepatitis 232.1%, and rates of pneumonia were 135.9%. An unexpected finding was that significantly higher risks for influenza in the group later diagnosed with cancer were only seen in the second and sixth years before diagnosis.
Drs. Inaida and Matsuno also observed greater associations between certain infections and certain cancer types. For example, the odds of influenza just before a cancer diagnosis were highest in those who developed male germ cell cancers (OR: 2.01; 95% CI: 1.31-3.09). The odds of pneumonia were highest in those who were diagnosed with stomach cancer (OR: 3.59; 95% CI: 2.04-6.30). Finally, the odds of hepatitis were highest in those who developed hematologic, blood, bone, and bone marrow cancers (OR: 19.04; 95% CI: 4.55-79.67), followed by liver, breast, and genitourinary cancers (OR: 11.60, 10.57, and 6.32, respectively). And, they found, the odds ratio for gastroenteritis was high for most cancers.
Keep an eye on increased infections?
But the association between infections and cancers is not as clear cut as one would believe.
“Interestingly, we found that infection afflicting a specific organ did not necessarily correlate with increased risk of cancer in the same organ,” commented Dr. Inaida. For instance, consider the link between pneumonia and stomach cancer mentioned above.
As researchers continue to unravel the infection/cancer connection, clinicians may want to keep tabs on the incidence of influenza, pneumonia, hepatitis, and gastroenteritis in their patients, the researchers indicated. More frequent infections may be useful in signaling patients at higher risk for cancers.
“These findings suggested that the annual assessment of these four infectious diseases could potentially be useful in examining the precancerous status for adults. Likewise, an increase of infection could be a sign of cancer development and inclusion of clinical immune suppression assays may further help early cancer detection,” concluded Dr. Inaida and Matsuno.