Which immunohistochemical markers would confirm the interpretation of a pediatric lung nodule with bloody cough?

• A. TTF-1, Napsin A
• B. p63/p40, CK 5/6
• C. Synaptophysin, chromogranin
• D. Napsin A, p63

Answer: (C)

Immunohistochemical profiling helps identify the tumor’s differentiation. In a pediatric lung nodule with hemoptysis, a neuroendocrine tumor such as a bronchial carcinoid is a key consideration. Neuroendocrine tumors characteristically express markers like synaptophysin and chromogranin. Their positivity supports neuroendocrine differentiation and points away from other lung lineages, such as adenocarcinoma (which would typically show TTF-1 and Napsin A) or squamous-type lesions (which would show p63/p40 and CK5/6). Therefore, staining positive for both synaptophysin and chromogranin best fits the expected neuroendocrine profile in this scenario.