Dysfunctional telomeres in human BRCA2 mutated breast tumors and cell lines

► Telomere dysfunction was detected in BRCA2 mutated breast tumors and cell lines. ► Chromosome end-to-end fusions were significantly higher in BRCA2 mutated breast tumors compared to sporadic tumors. ► Telomere sister chromatid exchanges and interstitial telomeric sequences were increased in BRCA2 heterozygous breast cell lines. ► Telomere dysfunction-induced foci were prominent in the BRCA2 heterozygous breast cell lines. ► The results indicate telomere dysfunction in association with capping defects and chromatid type aberrations in BRCA2 mutated breast tumors and cell lines.