Early immunoscintigraphic localisation of a mediastinal tumour with indium 111-DTPA CEA-specific F(ab')2 monoclonal antibody fragments (BW 431/31) using second tracer isocontour technique.

A female patient with steadily increasing carcinoembryonic antigen (CEA) serum levels of unknown origin was referred for immunoscintigraphy with indium 111-labelled CEA-specific monoclonal antibody. The procedure revealed a tumour, undetectable by conventional diagnostic methods. Anatomical landmarking using the second tracer isocontour technique allowed the distinction between an intra- or extrapulmonary lesion. Two months later, tumour infiltration along the aortic arch was confirmed by a targeted angio-CT scan. Upon surgery, the diagnosis was definitely established histologically (undifferentiated, solid large cell carcinoma, most probably arising from the bronchus), and staining by CEA-specific immunohistochemistry confirmed the presence of the CEA antigen.