Does getting a flu shot every year help prevent cancer?

Question

Marketwatch's story "10 surprising steps to staying cancer-free" states that getting an flu shot every year help prevent cancer:

Get an annual flu shot. Having the flu triggers inflammation, which can set the body up for serious problems when it’s most vulnerable, he says. The flu vaccine, whose contents change every year according to the dominant viral strains projected to circulate, helps the body tone down its harsh immune response. “I want [people] to think of a flu shot in terms of not just what it means today but a decade from now,” [Dr. David Agus, oncologist, professor of medicine at UCLA] says.

Does avoiding the flu reduce the risk of cancer?

Answer 1

The claim is made that having regular influenza vaccinations helps one stay free of cancer. However, a search of PubMed reveals no such study to support the assertion.

Could influenza viruses cause cancer then? So, preventing their infection would then lower the risk for cancer? However, influenza viruses are not known amongst those known to contribute to cancer: [1]

About 15-20% of human cancers worldwide have viral etiology. Emerging data clearly indicate that several human DNA and RNA viruses, such as human papillomavirus, Epstein-Barr virus, Kaposi's sarcoma-associated herpesvirus, hepatitis B virus, hepatitis C virus, and human T-cell lymphotropic virus, contribute to cancer development

We do know that chronic inflammation can cause cancer, but as it says in this article [2]

Chronic inflammation may be a causative factor in a variety of cancers. In general, the longer the inflammation persists, the higher the risk of cancer. Hence, acute inflammation, such as occurs in response to a transient infection, is not regarded as a risk factor for the development of neoplasia, although many of the same molecular mediators are generated in both acute and chronic inflammation. In general, inflammatory leukocytes such as neutrophils, monocytes, macrophages, and eosinophils provide the soluble factors that are thought to mediate the development of inflammation-associated cancer, although other cells, including the cancer cells themselves, also participate

and since the flu is clearly a transient infection, the claim is unsubstantiated.

[1] Poreba E, Broniarczyk JK, Gozdzicka-Jozefiak A. Epigenetic mechanisms in virus-induced tumorigenesis. Clin Epigenetics 2011 Aug;2(2):233-47. doi: 10.1007/s13148-011-0026-6. PubMed PMID: 22704339.

[2] Shacter et al. Chronic Inflammation and Cancer Review Article | January 31, 2002 | Colorectal Cancer, Oncology Journal

Answer 2

Here are two studies that say getting the flu (for real, not vaccine) reduces cancer risk in some types of cancer by 30% or more.

Common infections in the history of cancer patients and controls. J Cancer Res Clin Oncol. 1991;117(4):339-44.

The association between the frequency of manifest infectious diseases and cancer risk was investigated in a case-control study at Heidelberg, FRG. A total of 255 cases with carcinomas of the stomach, colon, rectum, breast, and ovary, as well as 255 population controls and 230 hospital controls were interviewed using a standard questionnaire. Controls were matched to the cases for age, sex, and region of residence at the time of the interview. A history of common colds or gastroenteric influenza prior to the interview was found to be associated with a decreased cancer risk. Thus the odds ratios for "three or more common colds per year (on average)" versus "no common cold within the last 5 years prior to the interview" were 0.18 (95% CI = 0.05-0.69) and 0.23 (95% CI = 0.06-0.89) relative to population controls and hospital controls, respectively.

Role of medical history in brain tumour development. Results from the international adult brain tumour study. Int J Cancer. 1999 Jul 19;82(2):155-60.

There was a statistically significant inverse association between glioma and all allergic diseases combined (RR = 0.59, 95% CI 0.49-0.71); this was also observed for specific allergic conditions, namely, asthma and eczema. Subjects who reported a history of infectious diseases (e.g., colds, flu) showed a 30% reduction in risk (RR = 0.72, 95% CI 0.61-0.85).

The wikipedia entry for oncolytic virus has this:

An oncolytic virus is a virus that preferentially infects and kills cancer cells.[1][2] As the infected cancer cells are destroyed by lysis, they release new infectious virus particles to help destroy the remaining tumour.[3] Oncolytic viruses are thought not only to cause direct destruction of the tumour cells, but also to stimulate host anti-tumour immune responses.[4][5]

AND a list of 9 current clinical trial using oncolytic viruses as cancer treatment.