P63 Differentiates Subtypes of Nonsmall Cell Carcinomas of Lung in Cytologic Samples Implications in Treatment Selection

BACKGROUND: Bevacizumab in combination with carboplatin and paclitaxel improves overall response and survival in patients with advanced or recurrent nonsmall cell lung carcinoma. However, this drug is not recommended in patients with squamous cell carcinoma or neoplasms with a dominant squamous component, Therefore, identification of squamous cell differentiation has therapeutic implications. In many instances, cytology is the diagnostic tool of choice: however, routine cytomorphology is limited in classification of nonsmall cell carcinomas into squamous and nonsquamous subtypes. The aim of this study was to identify the value of p63 immunocytochemical analysis in this distinction. METHODS: Review of cytology records identified 51 consecutive pulmonary specimens (16 fine needle aspiration samples, 15 washes, 12 brushes, and 8 lavages) with the diagnosis of nonsmall cell lung carcinoma (9 carcinomas with squamous differentiation and 42 carcinomas without squamous differentiation). Histologically, they all proved to be nonsmall cell carcinomas, 26 with squamous differentiation and 25 without squamous differentiation. p63 immunocytochemical stain was performed on archival alcohol-fixed Papanicolaou-stained cytology slides using standard immunocytochemical methods. RESULTS: Twenty-three (88 %) of the 26 histologically proven squamous cell carcinomas were positive for p63 on cytologic smears. By using p63 immunocytochemistry, the authors detected 14 carcinomas with squamous differentiation not identified by cytomorphology. Smears from all histologically proven carcinomas with squamous differentiation were positive for p63. Sensitivity of cytology for the detection of nonsmall cell carcinoma of lung with squamous differentiation increased from 35% to 88% using p63 immunocytochemistry (P = .001; McNemar test). The squamous component in 4 carcinomas was detected only in cytologic and not in corresponding histologic samples when subsequent p63 immunostaining was performed. CONCLUSIONS: The authors concluded that p63 is a useful marker for the detection of nonsmall cell carcinomas of lung with squamous differentiation when used in cytologic pulmonary samples. p63 immunocytochemistry significantly increases the sensitivity for the identification of lung neoplasms with squamous differentiation from 35% to 88% (P = .001). Therefore, p63 immunocytochemistry may be used in pulmonary cytologic samples of nonsmall cell carcinomas to identify squamous differentiation and to improve therapeutic selection of patients with lung cancer. Cancer (Cancer Cytopathol) 2009;117:46-50, (C) 2009 American Cancer Society.