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The “Old Friends Mechanism” and Cancer.


Defective immunoregulation and increases in inflammation-associated cancers


It is often assumed that all immunoregulation and Treg cells in cancer are bad for prognosis. However it is becoming increasingly clear that a failure of immunoregulation can lead to cancer, and can also drive the cancer after it has developed. Inflammation drives mutation and provides angiogenenic factors, and tumour growth factors. The increase in the incidence of some cancers (such as prostate) parallels the increases in other chronic inflammatory disorders. Similarly, colorectal cancer has a clear inflammatory component.


Infection, immunoregulation and cancer.


Rook GAW, Dalgleish A.
Immunological Reviews. (2011) 240:141-59.

Abstract
As man has moved rapidly from the hunter–gatherer envi- ronment to the living conditions of the industrialized countries, the incidences of some cancers have increased alarmingly. Recent increases are usually attributed to dietary changes or to altered exposures to putative carcinogens associated with the modern lifestyle. However, the changes in cancer incidence parallel similar increases in non-neoplastic chronic inflammatory disorders (inflammatory bowel disease, allergies, and autoimmunity), and the epidemiology is often strikingly similar. This parallel is worth exploring, because the increases in chronic inflammatory disorders are at least partly explained by immunoregulatory defects resulting from diminished exposure to microorganisms that co-evolved with mammals and developed a role in driving immunoregulatory circuits (the hygiene hypothesis). Dysregulated chronic inflammation can drive oncogenesis and also provides growth and angiogenic factors that enhance the subsequent proliferation and spread of tumor cells. Thus, a modern failure to downregulate inappropriate inflammation could underlie increases in some cancers in parallel with the increases in chronic inflammatory disorders. This possibility is supported by recent work showing that in some circumstances regulatory T cells protect against cancer, rather than aggravating it, as previously assumed. A greater understanding of these interactions might pave the way to improved microbe-based immunotherapies.

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Other authors have expressed very similar views :-

Microbial deprivation, inflammation and cancer.


von Hertzen LC, Joensuu H, Haahtela T.
Cancer Metastasis Rev. (2011) 30(2):211-23.

This paper can be found on PUBMED here