Which markers are included in the IHC panel for primary lung small cell carcinoma?

• A. synaptophysin, chromogranin A, CD56, Ki-67, MIB1, aP1
• B. synaptophysin, chromogranin A
• C. TTF-1, Napsin A, CK7, CK20
• D. p63, p40, CK5/6

Answer: (A)

Small cell lung carcinoma is a neuroendocrine tumor with a very high proliferation rate. The best IHC panel to support this diagnosis includes neuroendocrine markers that are typically positive in SCLC—synaptophysin, chromogranin A, and CD56—along with a proliferation marker showing an extremely high Ki-67 (MIB-1) labeling index. This combination highlights neuroendocrine differentiation and the aggressive growth pattern that define small cell carcinoma, helping distinguish it from other lung cancers that rely on different marker profiles. Other panels emphasize markers like TTF-1, Napsin A, CK7/CK20 for adenocarcinoma or p63/p40 and CK5/6 for squamous cell carcinoma, which are not the defining features of SCLC.