In the SCCA versus SCC differential diagnosis, p40 and K903 are each marginally more sensitive (92%) than p63 (88%), whereas CK5/6 boasts the greatest specificity (98%). p63's poor specificity (66%) can be improved to 94%, if an H-score ≥150 is used as the cutoff for a positive result.
Pulmonary neuroendocrine tumors also show p63 staining in some instances, particularly in higher-grade tumors, and the majority of small cell carcinomas are p63-positive.