In a mediastinal lymph node biopsy from a lung cancer patient, which markers support squamous differentiation?

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

Answer: (B)

Squamous differentiation is identified by markers that are characteristic of squamous epithelium. Nuclear p63 and its more specific isoform p40 are strongly expressed in squamous cell carcinomas, and CK5/6 are high‑molecular-weight cytokeratins typical of squamous lineage. When a mediastinal lymph node metastasis from lung cancer shows positivity for p63/p40 and CK5/6, it supports a squamous phenotype.

Markers like TTF-1 and Napsin A indicate adenocarcinoma of the lung, so their presence would argue against squamous differentiation. Neuroendocrine markers such as synaptophysin and chromogranin point toward neuroendocrine tumors, not squamous differentiation.