Cancer prevention strategies may need fundamental revision following evidence that cells with intact DNA repair systems can still suffer catastrophic genetic damage. This challenges the long-held assumption that functional BRCA pathways reliably protect against the DNA instability that drives tumor formation.
The culprit is EXO1, a nuclease enzyme found overproduced in numerous tumor types. When present at elevated levels, EXO1 aggressively degrades newly synthesized DNA strands during replication, creating double-strand breaks and genomic chaos. This destruction occurs through collaboration with MRE11, another DNA-processing enzyme, and happens regardless of whether cells possess working BRCA1 and BRCA2 genes. The research demonstrates that EXO1 overexpression renders cells hypersensitive to DNA-damaging treatments, mimicking the vulnerability typically seen only in BRCA-deficient cancers.
This finding expands our understanding of how genomic instability emerges in human cancers. Previously, researchers focused primarily on loss-of-function mutations in tumor suppressor genes like BRCA1/2. The discovery that overactive DNA repair enzymes can paradoxically destabilize genomes introduces a gain-of-function mechanism for cancer development. Since EXO1 overexpression appears more frequently in tumors than BRCA pathway inactivation, this represents a potentially major pathway to malignancy. The research suggests that monitoring EXO1 expression levels could identify high-risk patients who might benefit from targeted interventions, even when standard genetic testing shows normal BRCA function. For personalized medicine approaches, this adds another layer of complexity to predicting which patients will develop treatment resistance or secondary cancers.