Cancer Risks

The incidence of cancer in veterinarians is generally low, in part due to the low prevalence of cigarette smoking in this group. However, they come into contact with several potentially carcinogenic exposures including radiation, anesthetic gases, pesticides, and zoonotic agents. Other sources of carcinogenic exposure are solar radiation, veterinary pharmaceuticals, and office and laboratory chemicals (25).

Veterinarians have elevated risks for several specific cancer types including leukemia, Hodgkin's disease, non-Hodgkin's lymphoma, multiple myeloma, and cancers of the lip, stomach, prostate, brain, and connective tissue. Two major groups of risk factors have been proposed as causes of hematological malignancies in agricultural workers. The first group includes various agricultural chemicals. In particular, several studies have found increased risks of malignant lymphoma and soft tissue sarcoma in persons exposed to phenoxy herbicides. However, the evidence is inconsistent, and there is a wide variation in relative risk estimates. The second group of risk factors includes various animal viruses. There is currently little evidence concerning the zoonotic nature or human carcinogenicity of these viruses. However, an association has been suggested by recent evidence of increased risks of hematologic malignancies in abattoir workers, veterinarians, and meat inspectors. A third hypothesis, for which little evidence is currently available, is that agricultural work may involve prolonged antigenic stimulus leading to lymphoprolifera-tion. The factors responsible for the increased risks for cancers other than hematologic malignancies are not well understood but may also involve exposure to chemicals or viruses (26).

Using the Swedish Cancer Environment Registry, researchers compared the incidence of cancer among male veterinarians with that in the rest of the population. Veterinarians experienced increased risk of esophageal, colon, pancreatic, and brain cancers, and melanoma of the skin. The increased risks did not seem to be explained by the high socioeconomic status of this occupational group, and it was postulated that some of these results reflected the carcinogenicity of occupational exposures, including animal viruses, solar or ionizing radiations, and anesthetics (27).

A study of 450 California veterinarians who died between January 1960 and December 1992 demonstrated that in comparison to the California general population statistics, white male veterinarians had significantly elevated mortality from malignant melanoma of the skin, cancer of the large intestine, and rheumatic heart disease. Significantly elevated ratios were noted for deaths due to malignant melanoma of the skin and rheumatic heart disease in veterinarians in the profession 20 years or more; and cancer of the large intestine in veterinarians in the profession 30 years or more (23).

In the United States a cancer surveillance investigation using death certificates from 24 states for the period 1984 to 1989 was used to identify multiple myeloma and occupation associations. Women demonstrated significant excess risk among managers and administrators, post-secondary school teachers, elementary school teachers, social workers, other sales workers, waitresses, and hospital maids. Men showed significant risks among computer system scientists, veterinarians, elementary teachers, authors, engineering technicians, general office supervisors, insurance adjusters, barbers, electronic repairers, supervisors of extracting industries, production supervisors, photoengravers, and grader/dozer operators (28).

Studies of the Danish Cancer Registry on the possible association between exposures of parents at the time of conception and cancer in their offspring have provided no clear answer. Significantly increased risks for renal cancer (mainly Wilms' tumor) and for osteogenic and soft tissue sarcomas were observed in children in association with mothers' employment in medical and dental care. The risk for cancers at all sites was significantly elevated in children of female nurses and of male and female physicians, dentists, dental assistants, veterinarians, and pharmacists combined. Handling of drugs and exposure to anesthetics and infections during pregnancy are suggested to be potential risk factors. The suggestion in earlier studies that exposures to hydrocarbons and lead are risk factors for childhood cancer could not be supported by the analysis (29).

Causes of death among 5,016 white male veterinarians were compared to a distribution based on the general U.S. population. Proportions of deaths were significantly elevated for cancers of the lymphatic and hematopoietic system, colon, brain, and skin. Fewer deaths were observed than expected for cancers of the stomach and lung. Although socioeconomic and methodological factors may be involved, the patterns suggest that sunlight exposure is responsible for the excess of skin cancer among veterinarians whose practices are not exclusively limited to small animals, and ionizing radiation exposure contributes to the excess of leukemia among veterinarians practicing during years when diagnostic radiology was widely used (30).

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