Value of P63 and CK5/6 in distinguishing squamous cell carcinoma from adenocarcinoma in lung fine‐needle aspiration specimens

Abstract The current FDA‐approved standard of care for nonsmall cell lung cancer is Carboplastin/Taxol/Avastin based upon an impressive survival benefit; however, patients with squamous carcinoma (SQCC) cannot receive Avastin because of a 30% mortality rate due to fatal hemoptysis. In this study we evaluated the role of cytomorphology and immunohistochemistry in differentiating SQCC from adenocarcinoma (ADC) in lung FNA specimens. The case cohort included 53 FNA cases of nonsmall cell lung carcinoma with surgical pathology follow‐up. All FNA specimens were reviewed independently by a panel of cytopathologists to differentiate between SQCC and ADC. The cell block material was available in 23 cases (11 ADC and 12 SQCC) to perform immunohistochemical stains for TTF‐1, CK7, CK20, P63, and CK5/6. On surgical resection, 35/53 (66%) cases were diagnosed as ADC and 18/53 (34%) as SQCC. The number of cases classified correctly on the basis of cytomorphology was 66% for ADC and 53% for SQCC (combined accuracy 60%). By immunohistochemical staining, 14/23 (61%) cases expressed TTF‐1. Nine cases were TTF‐1 negative; eight of the TTF‐1 negative cases (89%) were SQCC. Twenty‐three cases expressed CK7 (87%); one ADC case (4%) showed focal CK20 positivity. Both P63 and CK5/6 expression was seen in 9/12 (75%) SQCC cases; none of the ADC cases showed this dual expression. Cytomorphology alone may not be able to stratify all cases of nonsmall cell lung carcinoma into ADC and SQCC in FNA specimens. The immune‐panel of TTF‐1, CK7, CK20, P63, and CK5/6 is useful in differentiating SQCC from ADC. Diagn. Cytopathol. 2009. © 2009 Wiley‐Liss, Inc.