SUB1 and neoplasm: Some studies have hypothesized that this nuclear protein is a tumor suppressor because PC4 prevented mutagenesis and killing by oxidative DNA damage.18,24 Other studies have shown that PC4 protein expression is upregulated in non-small cell lung cancer and could be an attractive new therapeutic target for the treatment of NSCLC.25 Up to now, however, the significance of PC4 expression in ESCC tissue and its effect on prognosis and therapy response have not been elucidated.