Chromogranin A in familial pheochromocytoma: diagnostic screening value, prediction of tumor mass, and post-resection kinetics indicating two-compartment distribution.

PURPOSE: Chromogranin A, co-released with catecholamines from the adrenal medullary and sympathetic neuronal vesicles, is elevated in plasma from patients with pheochromocytoma. We assessed its diagnostic screening value, its plasma level in correlation with tumor mass, and its disposition kinetics in familial pheochromocytoma and sporadic pheochromocytoma. PATIENTS AND METHODS: The sensitivity and specificity of chromogranin A's diagnostic value for pheochromocytoma were established through one kindred with familial pheochromocytoma associated with von Hippel-Lindau syndrome (13 available members) and in seven subjects with sporadic pheochromocytoma. Serial postoperative plasma samples were also obtained (5 minutes to 4 days) from eight subjects with pheochromocytoma in order to study chromogranin A post-resection kinetics. Chromogranin A was measured by radioimmunoassay based on purified pheochromocytoma chromogranin A.
RESULTS: In this kindred, elevations of chromogranin A (greater than 52 ng/mL) were sensitive (83%, five of six) and specific (100%, 10 of 10) in detecting familial pheochromocytoma; these diagnostic values comparable to those achieved by conventional evaluations for pheochromocytoma, such as urinary catecholamines, urinary catecholamine metabolites or imaging methods. Elevated levels of plasma chromogranin A specifically indicated pheochromocytoma, rather than von Hippel-Lindau syndrome gene carrier status. In 13 preoperative subjects with either familial or sporadic pheochromocytoma, plasma chromogranin A concentration predicted tumor size (r = 0.81, p less than 0.01). The change in chromogranin A plasma concentration after pheochromocytoma resection best fit a two-compartment model, with an initial rapid half-life time of 16 minutes, followed by a longer half-life time of 520 minutes. The model also predicted a 23.8:1 compartmental ratio of extravascular/intravascular chromogranin A, suggesting substantial tissue sequestration or binding of chromogranin A.
CONCLUSIONS: (1) Plasma chromogranin A is a valuable (sensitive and specific) diagnostic tool in detecting both familial and sporadic pheochromocytoma. (2) The concentration of plasma chromogranin A predicts the size of the pheochromocytoma. (3) Chromogranin A post-resection kinetics suggest extravascular sequestration of chromogranin A.