SOX2 and squamous cell carcinoma: Additionally 17/20 squamous tumors, and 2/20 for adenocarcinomas stained positively for p63 (Trp63), a protein involved in the self-renewal of stratified epithelial progenitors [22] and a frequent marker of squamous cell cancer that clusters closely with SOX2. In 14 of 20 squamous tumors, there was positive staining for both Sox2 and p63.