Endocrine Abstracts

Introduction: Neuroendocrine tumours (NETs) comprise a heterogeneous group of tumours that constitute a diagnostic and therapeutic challenge. The most commonly used general NET circulating biomarker is Chromogranin A (CgA). CgA is elevated under other circumstances, notably by the use of Proton Pump Inhibitors (PPIs) and possibly via a gastrin-mediated mechanism. Chromogranin B (CgB) and Cocaine- and Amphetamine-Regulated transcript (CART) are two less commonly used NET biomarkers. Some studies have reported that CgB levels might remain unaffected by PPI use; the effects of PPI use on CART have not previously been described.

Methods: Blood samples from 45 patients on PPIs and 43 controls were collected and analysed at NHS Trust outpatient clinics. Patients with a history of NET disease or with evidence of impaired renal function were excluded from the analysis. Plasma gastrin, CgA, CgB and CART levels were quantified by RIA. CgA levels were also measured using a commercially available ELISA kit (DAKO).

Results: CgB and CART levels did not differ significantly between PPI users and controls (P=0.576 and P=0.588 respectively). The same was true for CgA levels determined using our in-house RIA (P=0.207). This is in contrast to gastrin and CgA (DAKO) levels, which were significantly elevated in PPI users (both P<0.001). Furthermore, gastrin levels positively correlated with CgA (DAKO) levels (R=0.759, P<0.001).

Conclusions: CgB and CART levels remain unaffected by PPI use. However, we demonstrate significant differences in the effect of PPI treatment on CgA measured by different assays. Further work is now required to determine the utility of these biomarkers in the diagnosis of NETs in PPI users.