For this blog, I’m departing from my usual prostate cancer themes. This blog branches out more broadly on how infections may influence the development of cancer in general. We already know that cervical cancer is connected to the human papillomavirus, people with hepatitis B or C are more prone to liver cancer, and the human herpes virus 8 appears to increase the chances for Kaposi sarcoma. These are very specific relationships.

It now appears that there may be a previously unsuspected relationship between influenza, pneumonia, etc. and cancer risk. An April, 2020 journal article addresses from demographic statistics.^[i] What’s especially interesting about the findings is that the site of the infection (e.g. pneumonia in the lungs) is not necessarily specifically linked with cancer in that location. The cancer could occur somewhere else.

For their research, two Japanese scientists combed through tens of thousands of medical claims records over a 7-year period for people ages 30 and older. Of their total population of 50,749 patients, 2,354 had their first cancer diagnosis in the seventh year of the study, while the control group of 48,395 people had no cancer diagnosis at the end of the same period.

Connecting infections with cancer occurrence

What were the scientists looking for? They were exploring a possible link between having an infection—particularly flu, bacterial or viral infection of the stomach or intestines (gastroenteritis), infection of the liver (hepatitis), or pneumonia—and developing cancer within seven years.

In the years leading up to the seventh year, the authors noted that the cancer patients developed a greater number of infections than persons in the control group. The prevalence of those infections increased over the duration of the study period. The most common cancers that occurred were located in the stomach/intestinal tract, head and neck. The authors noted, “For each cancer site, an increased rate of infection prior to cancer diagnosis was observed.” Certain infections were associated with certain cancer types:

For example, the odds of influenza just before a cancer diagnosis were highest in those who developed male germ cell cancers …The odds of pneumonia were highest in those who were diagnosed with stomach cancer … Finally, the odds of hepatitis were highest in those who developed hematologic, blood, bone, and bone marrow cancers … And, they found, the odds ratio for gastroenteritis was high for most cancers.^[ii]

What’s the explanation?

Today, we know more about the body’s immune system than ever before, yet we still don’t fully understand enough to explain why one person shrugs off an infection like the flu while another person becomes desperately ill. Bacteria, viruses or other microorganisms that cause infection are called pathogens. When pathogens invade the body and multiply, the immune system mounts a protective defense in the form of inflammation. Inflammation can be acute (immediate but short-term response that may resolve the problem) or chronic (lingering, long-term response that may or may not resolve the problem). If inflammation becomes severe, it can set up general reactions in the body as the immune system struggles and demands more resources.

We know that cancer can grow in an environment of inflammation. I have previously written about the link between prostate inflammation and cancer. However, we still have a way to go before we’re able to connect the dots between something like the flu or hepatitis and a later emergence of, say, colon cancer. As the lead author of the study, Shinako Inaida, PhD, states, “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…”^[iii] The authors theorize that an increase in the prevalence of infection during the precancerous stage, especially the year before, may affect a person’s body in a way similar to cancer’s mechanism of suppressing the immune system, leaving the path open for cancer to develop in that individual. They also suggest that if a doctor notes an increase in infections in a given patient, it could be a sign of cancer development. It could well be worth it to test for clinical immune suppression as a form of early cancer detection.

Finally, as our knowledge about infection and the immune system deepens, there will always be individual exceptions, since each of us is a unique combination of genes, environment, etc. Even in identical twins, who share the same genes, gene expression can differ in such a way that one twin develops an autoimmune disease or cancer but the other remains healthy.

As long as scientists like Inaida and Matsuno continue to explore the mysteries of the human body, we can continue to hope that one day we will have explanations that will benefit all humankind.

NOTE: This content is solely for purposes of information and does not substitute for diagnostic or medical advice. Talk to your doctor if you are experiencing pelvic pain, or have any other health concerns or questions of a personal medical nature.

[i] Inaida S, Matsuno S. Previous Infection Positively Correlates to the Tumor Incidence Rate of Patients with Cancer. Cancer Immunol Res. 2020 Apr 17.
[ii] Meszaros, Liz. New study links common infections with specific cancers. MDLinx, Apr. 27, 2020. https://www.mdlinx.com/internal-medicine/article/7008
[iii] Ibid.