ERCC1 mRNA levels in lymphocytes correlate positively with DNA repair capacity measured by host cell reactivation. ERCC1 mRNA levels correlate closely with XPD, OGG1 and RAI mRNA levels in lymphocytes.

In case-control studies of lung cancer patients, lung cancer patients were shown to have lower mRNA levels and lower DNA repair capacity than healthy controls. This was also found in a case-control study of head and neck cancer. However, in a prospective study of lung cancer, persons, who were later diagnosed with lung cancer did not have a lower ERCC1 mRNA level than those who did not get lung cancer, indicating that the low ERCC1 expression level observed in cancer patients may be a result of the disease rather than a cause.

ERCC1 expression seems to be inducible at least at the mRNA level. Thus, the expression of ERCC1 in human lymphocytes correlated with increased solar influx indicating that UV irradiation may induce ERCC1 expression. In mice, X-ray irradiation lead to increased ERCC1 expression in lung tissue, and ingestion of diesel exhaust particles increased ERCC1 expression in liver. This indicates that ERCC1 expression is inducible, and thus that ERCC1 expression levels may rather be a biomarker of the internal dose of DNA damage than a biomarker of DNA repair capacity or a mix of the two.