In BRCA1 and BRCA2 breast cancers, chromosome breaks occur near herpes tumor virus sequences

Inherited mutations in BRCA1 and BRCA2 genes increase risks for breast, ovarian, and other cancers. Both genes encode proteins for accurately repairing chromosome breaks. If mutations inactivate this function, broken chromosome fragments get lost or reattach indiscriminately. These mistakes are characteristic of hereditary breast cancer. We tested the hypothesis that mistakes in reattaching broken chromosomes preferentially occur near viral sequences on human chromosomes. We tested millions of DNA bases around breast cancer breakpoints for similarities to all known viral DNA. DNA around breakpoints often closely matched the Epstein-Barr virus (EBV) tumor variants HKHD40 and HKNPC60. Almost all breakpoints were near EBV anchor sites, EBV tumor variant homologies, and EBV-associated regulatory marks. On chromosome 2, EBV binding sites accounted for 90% of breakpoints (p<0.0001). On chromosome 4, 51/52 inter-chromosomal breakpoints were close to EBV variant sequences. Five viral anchor sites at critical genes were near breast cancer breakpoints. Twenty-five breast cancer breakpoints were within 1.25% of breakpoints in model EBV cancers. EBV-like sequence patterns around breast cancer breakpoints resemble gene fusion breakpoints in model EBV cancers. All BRCA1 and BRCA2 breast cancers had mutated genes essential for immune responses. Because of this immune compromise, herpes viruses can attach and produce nucleases that break chromosomes. Alternatively, anchored viruses can retard break repairs, whatever the causes. The results imply proactive treatment and prevention of herpes viral infections may benefit BRCA mutation carriers.