The utility of <scp>TTF</scp> ‐1, napsin A, <scp>CK</scp> 5 and p63 staining in the sub‐classification of non‐small cell carcinoma of the lung

Background The potentially curative and/or palliative therapy for non-resectable lung cancer has evolved significantly over the past 2 decades. With the availability of targeted therapies, the need for precise sub-typing of non-small cell lung carcinoma (NCSLC) has become paramount. Objectives As there are few data from South Africa, we aimed to determine utility of TTF-1, napsin A, p63 and CK5 immunostaining on fine needle aspiration (FNA) cell block and formalin-fixed paraffin-embedded tissue biopsy specimens in subtyping NSCLC as adenocarcinoma and squamous cell carcinomas. Methods All cases of NSCLC diagnosed during a 3-year period were retrospectively identified. All FNA biopsy and formalin-fixed paraffin-embedded cases that were stained with TTF-1, napsin A, CK5 and p63 were collected. A lung cancer registry was used to access and correlate clinical and radiological data. Results We included 271 cases with diagnoses of adenocarcinoma of the lung (n = 201), squamous cell carcinoma of the lung (n = 53), unspecified NSCLC (n = 8) and other carcinomas (n = 9). TTF-1 and napsin A had sensitivities of 99.0% and 91.9%, respectively, positive predictive values (PPVs) of 90.8% and 90.3%, respectively, and accuracies of 91.0% for adenocarcinoma of the lung. Napsin A had a higher specificity than TTF-1 (90.2% vs 62.8%). Both CK5 and P63 had high sensitivities (95.4% and 97.9%, respectively) and negative predictive values of 96.4% and 96.8%, respectively, for squamous cell carcinoma of the lung. CK5 had a higher specificity than p63 (84.4% and 61.2%, respectively), PPV (80.4% and 70.8%, respectively) and accuracy (88.8% and 79.2%, respectively) for squamous cell carcinoma. Conclusion All four immunostaining methods had high sensitivities. TTF-1 and napsin A both had high PPV and diagnostic accuracy for adenocarcinoma of the lung, whereas CK5 had an equally high PPV and accuracy for squamous cell carcinoma of the lung. The specificity of napsin A for adenocarcinoma was higher than that of TTF-1. The specificity of CK5 for squamous cell carcinoma was higher than p63.