Well, at the age of 68 I've called a lot of small cell carcinomas without the benefit of immunohistochemistry.

Having said that - the therapeutic stakes are just too high to forego any help you can get. Usually either synaptophysin and chromogranin will mark the tumor well enough to make the call. Some folks are adding CD56, with which I have no experience. Neuron specific enolase (NSE) is probably obsolete. A broad spectrum cytokeratin stain such as AE1/AE3 helps make sure it's an epithelial tumor, TTF-1 is of some help in assuring its lung, and a negative CD45 (Leukocyte Common Antigen, LCA) pretty much excludes lymphoma in this diagnostic situation.

The cost, both in money and in misery, is just too high to risk being wrong here. IHC is expensive, but a lot less expensive than the wrong treatment.

Bob Richmond
Samurai Pathologist
Knoxville TN

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