Fig. 4.

p53 immunohistochemistry (a–c) and TP53 mutation analysis (D) results of case A. (A) The black arrows point out the esophageal squamous cell carcinoma (ESCC), and the white arrows show Barrett’s esophagus (BE) glands. (B) p53 is strongly expressed in the ESCC arising in association with BE. (C) Absence of expression of p53 in the oral squamous cell carcinoma, indicating a null mutation. In the adjacent normal mucosa, weak staining of the basal cell layer is observed, as usually present, that serves as internal control for proper staining. (D) Deletion of 14 bp in exon 6 of the TP53 gene, which causes a change in frameshift reading and enables the reading of a stop codon 3 triplets after the first affected amino acid. This eventually results in a shorter, mutant and abrogated nonfunctional protein product.