PCNA and esophageal squamous cell carcinoma: Our prior study has confirmed the association between Nestin and ESCC, and the results of that study lead us to 3 conclusions: 1) Nestin can be expressed in ESCC tissues and cell lines; 2) Nestin-positive ESCC is associated with a poor prognosis; 3) A positive correlation between Nestin phenotype and tumor cell proliferation indexes (Ki67 and PCNA) indicated that Nestin may be involved in the malignant proliferation of ESCC.