Synaptophysin and chromogranin are not necessarily detected in identical cell populations. Each of these functions as a marker for both neural and neuroendocrine cells, but neither is expressed by all cells in a given tumor. Thus, their combined use increases overall sensitivity in arriving at such a diagnosis. However, when diagnosing Merkel cell carcinoma, for example, cytokeratin 20 is a far more sensitive marker, and thus, has largely replaced the use of these markers in establishing these types of diagnoses.
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