Cancer: genetic, environmental, and infectious risks

Oxford American handbook of oncology. Second Edition. Oxford University Press (2015)


Genetic risks

Individuals with certain genetic defects are more likely to get cancer. Highly penetrant gene mutations have been associated with multiple familial cancer syndromes associated with a wide range of cancer types.

  • These gene defects are transmitted as autosomal dominant traits, and individuals with these gene mutations usually have a very high risk of cancer during their lifetime.
  • However, the prevalence of these gene mutations is low, thus the total population risk attributable to these genes is also low.

Table 3.1 lists examples of highly penetrant, low-prevalence, cancer-associated genes. There are more than 20 genes in this category. Population studies have also implicated genetic variants (polymorphisms) with a lower risk of cancer but much higher prevalence. To date, none of these studies has been sufficiently replicated to help guide clinical practice.

Environmental risks

  • Several environmental factors are known to cause premalignant lesions; e.g., chewing tobacco frequently causes leukoplakia, which may progress to oral cancer.
  • Smoking and lung cancer: cigarette smoking remains the most important avoidable environmental carcinogen worldwide (see Smoking-related cancers, p. 40).
  • The association of ultraviolet (UV) light with skin cancer, including malignant melanoma, has been clearly demonstrated. The increasing incidence of malignant melanoma has been clearly linked to behaviors that increase the intensity and duration of sun exposure.

Table 3.1. Cancer types and associated genes

Cancer type Gene
Breast BRCA1, BRCA2
Colon AFP, MSH2
Melanoma CDKN2A, CDK4
Papillary renal cell met
Thyroid ret

Infectious causes of cancer

Viruses have been incriminated in the etiology of the following:

  • Hepatocellular carcinoma (HCC; hepatitis B and C viruses)
  • Cervical carcinoma (human papilloma virus [HPV] serotypes 16, 18, others)
  • Anal carcinoma (HPV)
  • Burkitt’s lymphoma (Epstein-Barr viruses [EBV])
  • Nasopharyngeal carcinoma (EBV)

Vaccines are available against some of these agents, but only hepatitis B and HPV vaccines have been tested long enough to show efficacy.

Helicobacter pylori has been linked to gastric carcinoma and early claims of eradication of the organism by antibiotics, and subsequent protection from cancer are being validated.

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