In vivo imaging of chromogranin A-positive endocrine tumours by three-step monoclonal antibody targeting.

The detection of chromogranins (Cg) by immunohistochemistry and serology represents a new in vitro diagnostic tool for endocrine tumours. We have recently reported on the feasibility of targeting chromogranin A (CgA) for in vivo detection of pituitary adenomas by immunoscintigraphy (ISG). The scintigraphic procedure, based on an anti-CgA monoclonal antibody and on the avidin-biotin three-step method (Cg-3S-ISG), was evaluated on a group of 29 consecutive patients with known or suspected endocrine tumours other than pituitary adenomas, i.e. medullary thyroid carcinoma, carcinoid, insulinoma and parathormone- or ACTH-producing tumours. Primary tumours (10) and recurrences (16) were visualised in 26 patients, whereas conventional imaging techniques (planar radiography, computerised tomography, magnetic resonance imaging and ultrasonography) failed to detect the tumour sites in ten of the same (Cg-3S-ISG-positive) patients. Therefore, these preliminary results indicate that Cg-3S-ISG, the first immunological method able to detect endocrine tumours in vivo, has a higher diagnostic accuracy than conventional imaging techniques (93.1% compared with 65.5%).