The utility of TTF ‐1, napsin A, CK 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 CK 5 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, CK 5 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 CK 5 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 CK 5 for squamous cell carcinoma was higher than p63.