- Genetic risk factors (cannot be altered)
- Genetics (mutated BRCA1, BRCA2, and/or other genes)  ~3%
- Environmental risk factors (non-genetic and possible to eliminate or avoid)
- Ionizing radiation (X-rays, Gamma rays, radon)  <2%
- Environmental chemicals in air, water, food, soil, dust, consumer products  ?%
- Long-term tobacco smoking  37%
2. Summary of Research on Relationship of BLV Infection to Breast Cancer
3. Is Evidence That BLV Might Be a Risk Factor for Breast Cancer Now Strong Enough to Consider Primary Prevention Strategies to Lower BLV Infection Rate in Humans?
- Determine how humans become infected with BLV so those routes of transmission can be intercepted. Among cattle, BLV is transmitted via milk, blood (biting insects, contaminated veterinary/farming equipment, in utero)  so it is likely humans are infected through these same bodily fluids. Estimated prevalence of BLV in US cattle herds is 84% of dairy herds and 38% of beef herds . However, BLV is inactivated by pasteurization of milk and thorough cooking of beef, so educating people not to drink raw milk products or eat raw or extremely rare beef would protect them against this route of transmission.
- Eliminate BLV infection from US cattle, a likely main source of BLV infection.
- Eliminate farm/ranch practices that spread BLV among animals (e.g., using the same veterinary and agricultural equipment on multiple animals without decontamination between individual animals).
- Submit blood specimens from each animal to a veterinary testing laboratory to test for BLV. Then completely separate the pastures, barns, and all equipment used for BLV-positive from those used for BLV-negative animals.
- Create the future herd only from negative animals. This strategy has already achieved successful eradication of BLV in cattle in Australia/New Zealand and 19 nations in Europe .
- An anonymous pilot survey was sent to all registered owners of California beef and dairy farms in hopes of gathering information about their farm practices, their knowledge of BLV and other cattle viruses, and their attitudes about testing and eliminating BLV from their herds. Interestingly, the response rate was 1/44(2%) for dairy farmers and 16/42 (38%) for beef farmers. This inversely corresponds to the known rate of BLV infection in dairy herds (84%) versus beef herds (38%) and suggests that dairy farmers may already be aware of the high rate of BLV infection in dairy herds and may be hesitant about responding to the questionnaire. The survey also indicated that the majority of the beef ranchers who responded were members of an agricultural organization, which might be a persuasive vehicle of gaining the cooperation of ranchers/farmers in any proposed BLV elimination program.
- The ideal solution for prevention of most infectious diseases is an effective vaccine which, in the case of BLV infection, could be used to vaccinate both cattle and humans. Initial attempts to develop an effective vaccine to protect cattle from BLV infection resulted in antibody formation Bovine leukemia virus associated with mammary epithelial cell proliferation in Argentinian women but did not protect against a challenge with infectious BLV injected later . This suggests that the only effective vaccine may have to be a live vaccine, which is much more complicated to develop. However, new strategies for an effective vaccine look promising. If more funding were available to support further research in this area, scientists would likely be more interested in live BLV vaccination development.
Conflicts of Interest
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|Source of Specimens/[Reference]||Sample Number/Specimen Type||Analysis Methods||Normal Tissue||Cancer Tissue||Odds ratio (Risk) (95% Confidence Internal)||Probability Happening by Chance *|
|1. Cooperative Human Tissue Network (Southern and Eastern Division ||n = 239/FFPE||IS-PCR||30/104 (29%)||67/114 (59%)||3.07 (1.66–5.69)||p < 0.001|
|2. Douglass, Hanley, Moir Pathology, Macquerie Park, NSW, Australia ||n = 96/FFPE||IS-PCR||19/46 (41%)||40/50 (80%)||4.72 (1.71–13.05)||p < 0.003|
|3. MD Anderson Cancer Center, Houston, TX ||n = 166/FFPE||IS-PCR||20/105 (19%)||35/61 (57%)||5.59 (2.76–11.30)||p < 0.0001|
|4. Argentina Buenos Aires/Tindal ||n = 85|
|IS-PCR||0||19/85 (23%)||Analysis not possible; no normal tissue available|
|5. Columbia Bogota ||n = 53||PCR||24/53 (45%)||20/53 (36%)||Analysis not performed by authors; normal tissue had higher % positive|
|6. Brazil, Rio Grande do Sul ||n = 144|
|IS-PCR NL-PCR||10/72 (14%)||22/72 (31%)||2.73 (1.18–6.29)||p < 0.027|
|7. USA, Mexico, Vietnam ||n = 51|
USA NCI DNA sequence data
|NGS||0||0/51 (0%)||Analysis not possible; no normal breast tissue sequences available|
|8. China ||n = 91|
|0||0/91 (0%)||Analysis not possible; no normal breast tissue available|
|Risk Factor||Referrant||High Risk Group||Risk *|
|Years on hormone replacement||None||5 years||1.3|
|Age at menarche||>15 years||<12 years||1.3|
|Age at natural menopause||<45||≥55 years||1.4|
|Years on oral contraceptives||none||>12 years||1.4|
|Age at first full-term pregnancy||<25 years||>35 years||1.8|
|First degree relative with BC||None||One||2.0|
|Mother/sister with breast cancer||Not present||Present||3.6|
|BLV in breast epithelium||Not present||Present||4.0 #|
|BRCA1 and BRCA2 genes||Not mutated||Mutated||4.7|
|Ionizing radiation||None||High dose||5.2|
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