| Little is known about the cause of prostate cancer compared to any other common cancer in the human body. There are no proven risk factors for the development of prostate cancer, but some risk factors have been proposed, although the findings are often weak and controversial.
Only two factors are proven to be essential for the development of prostate cancer: male hormones (testosterone, one type of androgen hormone) and age. The entire prostate requires hormones for growth and development, and these are also essential for cancer maintenance and growth.
Proposed risk factors for prostate cancer
Family History and Genetics: Familial predisposition with early onset of prostate cancer probably accounts for about 9% of cases, with increasing risk as the number of affected relatives increases. A man's risk is two-fold higher if a first degree relative such as a father or brother has prostate cancer, and the risk is 5-11 fold higher if 2 or 3 first degree relatives have cancer. Heredity appears to be one of the most consistent and strongest risk factors for the development of prostate cancer.
Diet: Dietary fat may also cause prostate cancer, according to cross-cultural comparisons, but the relationship is complex and ill-defined, perhaps due in part to the influence of diet on the production of sex hormones. Obesity and alcohol abuse may also be risk factors. One school of thought believes that high fat diet is a promoter of cancer after it has developed, accelerating its growth and aggressiveness so that it is more threatening.
Smoking: Prostate cancer is one of the few cancers in the human body which has not been strongly linked to smoking.
Viruses: Viral diseases such as Herpesvirus type 2 and Cytomegalovirus may be involved in prostate cancer, but the data are not conclusive. Human papillomavirus has been linked to a small number of cases of prostate cancer, and this is an area of active investigation. It should be noted that HPV has been conclusively linked to cervical cancer, raising the possibility of a sexually transmitted virus associated with cancer.
Venereal Diseases: Early studies which implicated venereal diseases such as gonorrhea have been refuted.
Sexual Activity: Some investigators have suggested that sexual abstinence may contribute to prostate cancer risk, but there is no consistent evidence to support this contention despite multiple studies in the past 30 years. There is also no apparent increase in risk for men who have had multiple sexual partners.
Occupation: Conflicting results have been obtained in the search for occupational exposure which increases the risk of prostate cancer. Farming has been named in many studies, perhaps due to contact with agricultural products or pesticides. Cadmium, rubber and zinc workers may be at increased risk, but this has been refuted. Those exposed to radiation, including survivors the the Hiroshima and Nagasaki atomic bomb blasts, have a significant increased risk of many cancers, including leukemia, but apparently not for prostate cancer.
Vasectomy: Surgical sterilization with segmental removal of the vas deferens (vasectomy) has been proposed as a risk factor for prostate cancer, but reports to date have been affected by patient selection bias. Further studies are needed to determine the validity of these findings; the level of risk, if confirmed, appears to be low. An expert panel convened by the National Institutes of Health in 1993 concluded that the possible increased risk of prostate cancer due to vasectomy was low or nonexistent, and there was no need to discontinue vasectomy or reverse the procedure in men as a preventive measure.
Benign Prostatic Hyperplasia (BPH): Benign prostatic hyperplasia (BPH) is frequently seen in association with prostate cancer, and there are a number of compelling similarities, including increasing incidence and prevalence with age, concordant natural history and hormonal requirements for growth and development. However, no causal relationship has been established.
Prostatic Intraepithelial Neoplasia (PIN): Patients with high-grade prostatic intraepithelial neoplasia (PIN) are at increased risk for prostate cancer, and many are found to have cancer on repeat biopsy. PIN can only be identified on needle biopsy. It is uncertain whether the linkage of PIN and cancer represents an etiologic link or association.
Old Age: Is prostate cancer an inevitable consequence of old age? If so, what are the changes that occur with aging which account for malignant change? Perhaps there is breakdown of the immune system, the surveillance system of the body which discards tens of thousands of damaged or mutated cells daily. It is also possible that the immune system is overwhelmed by an increased number of genetically altered cells in the body which occurs naturally with age. The number of altered or damaged cells may increase because of progressive failure of the superoxide dismutase and other enzymes which act on a cell-by-cell basis to deal with environmental damage such as carcinogens, high fat diet, and other factors. The cumulative exposure to mutagens and carcinogens could influence all of these factors, thereby leading to cancer.
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