The p63 + CK5 antibody multiplex stain has been especially designed for squamous cell carcinomas, particularly those derived in lung cancer. In-house studies has shown greater than 80% of squamous cell carcinoma of the lung were positive and other studies have shown that the combination of p63 and CK5 was useful for differentiating adenocarcinoma from squamous cell carcinoma with 100% specificity and 82% sensitivity, 89% specificity and 79% sensitivity, respectively. Studies have also shown that TTF-1 and Napsin A are highly specific and sensitive for lung adenocarcinomas. A critical assessment is essential for correct diagnosis because patients with squamous carcinoma (SqCC) cannot receive Avastin therapy due to a 30% mortality rate as a result of fatal hemoptysis (hemorrhaging). Therefore when used in a panel with TTF-1 + Napsin A, this unique antibody cocktail of p63 + CK5 should prove useful for immunohistochemical analysis of poorly differentiated lung adenocarcinomas versus squamous cell carcinomas in formalin-fixed paraffin-embedded tissues.