Expression of p63 in thymomas and normal thymus.

The p63 gene, a member of the p53 family, is an epithelial marker expressed in embryonic ectoderm, breast myoepithelium, prostate, oral epithelium, epidermis, and urothelium. The δN-p63 isoforms of p63, which are believed to behave as oncogenes, are expressed in squamous cell carcinoma, basal cell carcinoma, and transitional cell carcinoma. Only a few authors have looked for p63 expression in thymomas and normal thymus. We, therefore, thought of undergoing such a search by taking advantage of our archival material. We studied 66 cases of thymoma (1 type A, 8 type AB, 12 type B1, 19 type B2, 12 type B3, and 14 type C/thymic carcinoma) and 10 specimens of normal human thymus arranged in tissue microarrays. All thymomas (including thymic carcinomas) were positive for p63 regardless of type. Most of the epithelial cells of the normal thymus were also positive for this marker.