Which markers compose the IHC panel for primary lung squamous cell carcinoma?

• A. Napsin A, TTF-1, CK7
• B. p63, p40, CK5/6
• C. CK7, CK20
• D. synaptophysin, chromogranin A, CD56

Answer: (B)

The main idea is using immunohistochemistry to demonstrate squamous differentiation in lung tumors. For primary lung squamous cell carcinoma, the most informative panel includes p40, p63, and CK5/6.

p40 is the most specific marker for squamous differentiation, giving a strong indication of squamous lineage when positive. p63 is also commonly expressed in squamous cells and helps detect squamous features, but it can be seen in other contexts as well, so it’s most powerful when interpreted alongside other markers. CK5/6 are cytokeratins associated with squamous epithelium, and their positivity supports squamous differentiation as well.

In contrast, markers like Napsin A and TTF-1 (often with CK7) point toward lung adenocarcinoma, not squamous. Neuroendocrine markers such as synaptophysin, chromogranin A, and CD56 suggest neuroendocrine tumors rather than squamous cell carcinoma. CK7 and CK20 patterns are less definitive for distinguishing SqCC from other lung cancers.

Thus, the combination of p40, p63, and CK5/6 best identifies squamous cell carcinoma of the lung.