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Lung cancer is the second most common cause of cancer deaths in the U.S. Lung cancers exist as three subtypes: non-small cell lung cancers (NSCLC) — comprising the adenocarcinoma and squamous cell carcinoma subtypes, which together account for 75% of cases — and small cell lung cancers (of neuroendocrine origin), which account for the remainder.
The availability of targeted therapies makes it essential to correctly subtype NSCLCs. IHC markers such as NKX2-1/TTF-1, Napsin A, and surfactant protein A (adenocarcinoma), or p63, CK5/CK6, SOX2, and Desmoglein-3 (squamous cell carcinoma), can identify the subtype when the morphology is unclear or when a biopsy has insufficient material for diagnosis (Noh, 2012; Gurda, 2015). Small cell lung cancers can be identified with markers such as LMWK, CAM5.2, chromogranin, synaptophysin, CD56, and NKX2-1/TTF-1 (Travis, 2012).
Although platinum-based chemotherapy has been the standard treatment for metastatic NSCLC, lung cancers with mutations in the epidermal growth factor receptor (EGFR) and anaplastic lymphoma kinase (ALK) may respond to specific kinase inhibitors, so there is a need to identify the subset that carry these mutations (Cooper, 2011; Malhotra, 2017; Kumar, 2017).