Basaloid squamous cell carcinoma of lung shows strong diffuse positivity for p40 and p63 (shown here). CK5/6, CK10, CK14 are also expressed. TTF-1 is negative. About 10% of cases show focal positivity for neuroendocrine markers. p63 is a highly sensitive marker of squamous differentiation; however, it lacks specificity and is frequently expressed in large cell neuroendocrine carcinomas and large cell lymphomas of lung. p40 antibody, which recognizes an isoform of p63, has high sensitivity as well as specificity and is superior to p63 as a squamous marker. Image courtesy of: Jian-Hua Qiao, MD, FCAP, Los Angeles, CA, USA.