p40 is the Best Marker for Diagnosing Pulmonary Squamous Cell Carcinoma

Histologic distinction among non-small cell lung carcinomas, particularly between squamous cell carcinoma (SQC) and adenocarcinoma (ADC), has become more important. Recently, a p40 antibody was suggested to be a highly specific marker for SQC. We evaluated p40 expression and compared it with the expression of other SQC markers in 580 primary lung carcinomas, including 158 SQCs, 156 ADCs, 50 carcinoid tomors, 107 large cell neuroendocrine carcinomas, 68 small cell lung carcinomas, and 41 malignant mesotheliomas. Detailed histologic distributions of p40-positive cases were as follows: 153 (96.8%) of 158 SQCs, 7 (4.6%) of 152 ADCs, 0 (0%) of 50 carcinoid tomors, 4 (3.6%) of 107 large cell neuroendocrine carcinomas, 1 (1.5%) of 68 small cell lung carcinomas, and 1 (2.4%) of 41 mesotheliomas. p40 staining yields high sensitivity as well as high specificity for distinguishing SQC from ADC, neuroendocrine carcinomas, and malignant mesothelioma.