Patients with
neuroendocrine tumors are found with increasing frequency. Accordingly, knowledge about relevant
tumor markers and assays for diagnosis and control has become essential.
Neuroendocrine tumors release one or more
granin proteins. Of these,
chromogranin A (CgA) has so far become the most widely used general marker. The CgA
protein is, however, extensively cleaved and otherwise modified during the biosynthetic processing. In addition, the CgA-processing in individual
tumors varies considerably. But only few CgA-assays have taken the processing into account and characterized the assays with respect to precise
epitope-specificity. Consequently, we do not know which fragments most CgA-assays measure. It is therefore at present difficult to compare CgA-measurements from
tumor patients. Some
tumors, however, release - in addition to
granins - also a specific
hormone that causes a clinical syndrome. This review uses
gastrinomas (
gastrin-producing tumors) as a starting point for discussion of CgA versus
peptide hormone as
tumor marker. Data available so far indicate that well-defined assays for
gastrin have significantly higher diagnostic sensitivity than CgA measurements in
gastrinomas. But the review suggests that CgA-quantitation using processing-independent analysis (PIA) may provide an equally high diagnostic sensitivity and in addition offer a simple possibility for estimation of the
tumor-burden.