Which markers comprise the IHC panel for primary lung small cell carcinoma?

• A. synaptophysin, chromogranin A, CD56, Ki-67, MIB1, aP1
• B. Napsin A, TTF-1, Ber-Ep4, CK7
• C. TTF-1, CK7, CK20, CK5/6
• D. p63, CK5/6, CK7, CK20

Answer: (A)

Small cell lung carcinoma is a neuroendocrine tumor, so the IHC approach relies on markers that confirm neuroendocrine differentiation and a high proliferation rate. Neuroendocrine markers such as synaptophysin, chromogranin A, and CD56 reliably stain SCLC cells, supporting the diagnosis. A high Ki-67 labeling index is also characteristic, and Ki-67 is commonly assessed with the MIB-1 antibody to quantify proliferation. This combination—neuroendocrine markers plus a very high proliferation marker—best fits primary lung small cell carcinoma.

Other panels emphasize markers used to identify non-small cell lung cancers, like Napsin A and Ber-EP4 for adenocarcinoma or CK7/CK20 patterns and p63/CK5/6 for squamous differentiation, which do not capture the neuroendocrine phenotype of SCLC.