Results from a study published in Cancer Immunology Research, a journal of the American Association for Cancer Research (AACR), shows that patients experienced a greater occurrence of infections in the years preceding a cancer diagnosis.

“Cancer can develop in an inflammatory environment caused by infections, immunity disruption, exposure to chemical carcinogens, or chronic or genetic conditions,” noted Shinako Inaida, Ph.D., a visiting researcher at the Graduate School of Medicine at Kyoto University in Japan.

“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,” Inaida added.

“This information may contribute to efforts to prevent or detect cancer.”

“[A number of] studies have suggested an increase in infections prior to the development of non-solid tumors, such as lymphoma, chronic lymphocytic leukemia, and myeloma,  Inaida explained.

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“However, fewer studies have examined infection prior to the development of solid tumors.”

In a 7-year, retrospective, case-control, study, conducted between 2005 to 2012, Inaida along with Shigeo Matsuno, Ph.D., examined a large medical claims database of a Japanese social health insurance system of people ≥30 years of age on the prevalence of influenza, gastroenteritis, hepatitis, and pneumonia infections to indirectly examine whether these infections correlated to malignant cancer formation.

As part of their study the scientists determined the annual rate of infections in adults without any recorded immunodeficiencies were included in the study.

Malignant cancer
The case group was composed of 2,354 individuals who were diagnosed with any malignant cancer between July 2010 and June 2011, and the control group was composed of 48,395 individuals who were not diagnosed with cancer between January 2005 and December 2012.

The case group included 1,843 men and 511 women while the control group had 37,779 men and 10,616 women. The results demonstrated the average age of individuals in the case group to be 45.1 years. In contrast, the average age of people in the control group was 43.9 years.

The most common cancers diagnosed in the case group were digestive and gastrointestinal, head and neck, and stomach cancers. Other cancer types diagnosed in the case group included respiratory and thoracic, germ cell, genitourinary, liver, breast, hematologic, blood, bone, and bone marrow, endocrine and unknown or other cancers.

The authors found that individuals in the case group had experienced higher rates of infection over the six years prior to their cancer diagnoses than those in the control group over the same time period.

The largest differences in annual infection prevalence rates occurred in the sixth year, which was one year prior to a cancer diagnosis. During this year, the infection prevalence rates for the case group were higher than the control group by 18% for influenza, 46.1% for gastroenteritis, 232.1% for hepatitis, and 135.9% for pneumonia.

People in the case group, the age-adjusted odds of infection increased each year. During the first year, those in the case group had a 16% higher likelihood of infection than the control group, compared with a 55% greater risk in the sixth year. During the sixth year, the highest age-adjusted odds ratio was observed for hepatitis infection, with those in the case group having had a 238% higher likelihood of hepatitis infection than those in the control group.

The authors of the study also found that certain infections appeared to have a greater association with certain cancer types. The odds of influenza infection just before cancer detection, for example, were highest for those who developed male germ cell cancers.

In addition, the odds of pneumonia were highest in those who went on to develop stomach cancer, and the odds of hepatitis infection were highest in those who developed hematologic, blood, bone, or bone marrow cancers.

“Interestingly, we found that infection afflicting a specific organ did not necessarily correlate with increased risk of cancer in the same organ,” Inaida noted.

Study limitation
A limitation of the study was the lack of information about environmental exposures, lifestyles, or underlying genetic or medical conditions, which could have contributed to increased infection in addition to causing cancer. Another limitation was that information regarding infection was based solely on diagnoses recorded in the database; thus, there may be variability in diagnoses across different clinicians, and some infections may not have been diagnosed or recorded. The small sample size for rare cancers was an additional limitation.

[1] Inaida S., Matsuno S. Previous Infection Positively Correlates to the Tumor Incidence Rate of Patients with Cancer. Cancer Immunology Miniatures. DOI: 10.1158/2326-6066.CIR-19-0510

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