CD56

CD56 is a neural cell adhesion molecule (NCAM) and functions as a homophilic binding glycoprotein involved in cell to cell adhesion. In IHC, CD56 is a sensitive marker for neuroendocrine tumours including most small cell carcinomas and carcinoid tumours as well as a defining marker of natural killer (NK) cells and NK‑cell lymphomas. It may also be expressed in subsets of T‑cell lymphomas. Because CD56 is not specific for neuroendocrine differentiation, it must be interpreted alongside other neuroendocrine markers such as synaptophysin and chromogranin. CD56 shows membranous staining and is also normally expressed in peripheral NK cells, subsets of T lymphocytes, and neural tissues (1).

Recommended Controls

Criteria for acceptable staining is a membranous and/or cytoplasmic staining pattern. Appendix used in the survey material is a high expressor staining the peripheral nerves. It is recommended to include tonsil as it demonstrates both a positive control (moderate to strong membrane staining of natural killer (NK) cells) and a negative control all subtypes of lymphocytes.

Expected staining pattern

Adrenocortical tumour

Appendix

Liver

Appendix

Tonsil

Disclaimer

These methods are intended as a guide only. Laboratories that wish to implement these methods should perform internal validation/verification prior to use. The RCPAQAP does not make any claim or warranty for the accuracy or performance of these methods.