Chromogranin A: Its Role in Endocrine Function and as an Endocrine and Neuroendocrine Tumor Marker*

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Abstract
I. Introduction CHROMOGRANIN A (CgA) is a 49 kilodalton protein that is produced exclusively by endocrine and neuroendocrine cells (1–3). CgA was originally discovered in the chromaffin granules of the adrenal medulla, hence its name (1–3). The adrenal gland is the main organ source of CgA, where it is the major soluble protein of catecholamine secretory granules (2, 4). Furthermore, CgA is found in a variety of endocrine and neuroendocrine cells and tissues that have electron-dense core secretory granules and is absent in such tissues that do not; however, CgA is not present in exocrine cells (1–5). CgA has also been demonstrated in human neurons and in the central nervous system (1, 5, 6) and is present in submammalian species (7, 8). CgA is costored and cosecreted with the resident hormones of these secretory granules, such as catecholamines and calcitonin (CT) (9, 10). In these other endocrine sites, as in the adrenal medulla and thyroid C cells, CgA is in the same secretory granule as the associated hormones (9–11). The gene for CgA has been localized to chromosome 14 (12). Although the function of CgA is not known, it can serve as a tissue and serum marker for a variety of endocrine cells and tumors (9–15). Thus, the identification of CgA by immunohistology and the measurement of CgA by immunoassay represent new diagnostic tools for the endocrinologist (9, 16).

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