Abstract B30: Bovine leukemia virus in breast tissue linked to increased cell proliferation and breast cancer risk
Authors: Buehring Gertrude C. , Shen HuaMIn , Baltzell Kimberly , Sison Jennette , Krishnamurty Savitri , Lendez Pamela , Matinez-Cuesta Lucia , Nieto-Farias MariaVictoria , Dolcini GuillerminaLaura , Ceriani MariaCarolina 
Published: August 2018

Purpose: To compare recent data sets on frequency of bovine leukemia virus (BLV) detection in breast tissue in different human populations, and association of BLV with a confirmed diagnosis of breast cancer and expression of common clinical biomarkers. Many risk factors are associated with breast cancer, but what causes initial molecular/cellular changes from normal to malignant is not well understood. Six types of human cancer are caused by viruses, and several viruses have been studied for a role in breast cancer. BLV is a common virus of US cattle (38% of beef herds, 89% of dairy herds, 90-100% of large dairy operations). BLV DNA and protein were previously identified in human tissues.

Methods: Breast tissue specimens were archived formalin-fixed, paraffin-embedded tissue sections from sources mentioned below. In situ PCR (IS-PCR) was performed on intact deparaffinized sections on glass slides, using primers from the tax region (transforming gene), highly conserved and rarely deleted, as are most BLV genome regions as tumor progression occurs. BLAST sequence comparisons indicated primers had high homology only with BLV, and extremely low homology with human genomic sequences, including human endogenous retroviral sequences. Previous laboratory experiments confirmed this specificity and established appropriate controls for the assay. Sections were semiquantitatively scored for density of the digoxygenin-labeled IS-PCR product within mammary epithelial cells, upon microscopic examination by two independent examiners.

Results: Previous data sets using samples from the Cooperative Human Tissue Network, USA (n=239) and New South Wales, Australia (n=96), showed BLV presence significantly more frequently in malignant tissue than in normal breast tissue from women with no breast cancer history. Odds ratios (OR) and confidence intervals (CI) were 3.07(1.66-5.69), p≤.001 and 4.72(1.71-13.05), p≤.003, respectively. New unpublished data indicate specimens from MD Anderson Cancer Center in Houston, TX (n=216) show an even higher OR (CI) of 5.59 (2.76-11.30), p≤.0001. Argentinian specimens showed lower frequency (22%) in malignant tissues than US (58%) and Australian specimens (80%). Cell proliferation markers, KI67 and HER2 overexpression were significantly associated with BLV presence in Argentinian malignant breast tissues. For 31 Australian subjects with breast cancer, archived normal breast tissues were available from surgery 3-10 years previous for an unrelated condition. For 23 (74%) of these, BLV was already present in normal tissue at least 3 years before cancer diagnosis, consistent with a causative temporal relationship between BLV presence and subsequent cancer development.

Conclusions: New unpublished data indicate BLV in some Argentinian women, but the frequency in breast cancer tissue is lower than in US and Australian women. Tests for conventional prognosis/proliferation biomarkers (ER, PR, HER2, Ki67) in Argentinian specimens showed BLV presence significantly associated with moderate-high Ki67 level (p≤0.009) and HER2 overexpression (p≤0.0442), consistent with possible BLV role in enhanced cell proliferation. BLV’s mode of transformation is via the oncogenic protein (Tax), which inhibits host cell DNA repair via the base excision pathway. DNA damage observed in breast cancer cells, including driver mutations, could theoretically have been initiated due to DNA repair inhibition by BLV infection. Elucidating initiators for any cancer opens opportunities for primary and secondary prevention. For viruses, the reservoir (e.g., BLV-infected cattle) could be reduced, transmission to humans could be intercepted (e.g., education to avoid raw milk, raw beef appetizers), vaccines could be developed, and elimination of the virus might be achieved by developing BLV-targeting agents. Driver mutations already initiated by BLV might be targeted as part of personalized secondary prevention and/or therapy.

Note: This abstract was not presented at the conference.

Citation Format: Gertrude C. Buehring, HuaMIn Shen, Kimberly Baltzell, Jennette Sison, Savitri Krishnamurty, Pamela Lendez, Lucia Matinez-Cuesta, MariaVictoria Nieto-Farias, GuillerminaLaura Dolcini, MariaCarolina Ceriani. Bovine leukemia virus in breast tissue linked to increased cell proliferation and breast cancer risk [abstract]. In: Proceedings of the AACR Special Conference: Advances in Breast Cancer Research; 2017 Oct 7-10; Hollywood, CA. Philadelphia (PA): AACR; Mol Cancer Res 2018;16(8_Suppl):Abstract nr B30.