Abstract
Bovine leukemia virus (BLV), a common virus of cattle globally, was believed for decades not to infect humans. More recent techniques (in situ PCR and DNA sequencing) enabled detection of BLV in human breast tissue, and determination of its significant association with breast cancer in a US population. Using similar techniques to study 96 Australian women, we report here detection of retrotranscribed BLV DNA in breast tissue of 40/50(80%) of women with breast cancer versus 19/46(41%) of women with no history of breast cancer, indicating an age-adjusted odds ratio and confidence interval of 4.72(1.71–13.05). These results corroborate the findings of the previous study of US women with an even higher odds ratio for the Australian population. For 48 of the subjects, paired breast tissue samples, removed 3–10 years apart in two unrelated procedures, were available. For 23/31 (74%) of these, in which the first specimen was diagnosed as nonmalignant (benign or premalignant) and the second as malignant, BLV was already present in benign breast tissue years 3–10 years before the malignancy was diagnosed. This is consistent with the supposition of a causative temporal relationship between BLV infection and subsequent development of cancer.
Highlights
Australia has a high female breast cancer incidence
Studies of descendants of Asian immigrants to countries with a Western culture, revealed rates of breast cancer increasing with each generation [3], leading to the hypothesis that changes in reproductive patterns, use of exogenous female hormones, and/or diet contributed to increased breast cancer incidence
There was no conspicuous morphologic difference between individual Bovine leukemia virus (BLV)-infected versus uninfected mammary epithelial cells within breast tissues of any diagnosis
Summary
Australia has a high female breast cancer incidence. Together with New Zealand, it ranks third in regional age-standardized per capita incidence globally [1]. Incidence of breast cancer in New South Wales, where one third of the Australian population resides, has been rising steadily since 1983 [1]. Studies of descendants of Asian immigrants to countries with a Western culture, revealed rates of breast cancer increasing with each generation [3], leading to the hypothesis that changes in reproductive patterns, use of exogenous female hormones, and/or diet contributed to increased breast cancer incidence. Global statistics indicate a striking geographical correlation between breast cancer incidence and milk consumption [4,5].
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