ISSN 1470-3947 (print) | ISSN 1479-6848 (online)

Endocrine Abstracts (2008) 16 S30.3

[123I]Iodometomidate as a radiotracer for diagnosis of adrenal tumours and adrenocortical carcinoma

Stefanie Hahner1, Andreas Schirbel2, Michael Kreissl2, Martin Fassnacht1, Sarah Johanssen1, Felix Beuschlein3, Marcus Quinkler4, Martin Reincke3, Andrea Stuermer1, Christoph Reiners2 & Bruno Allolio1

1Department of Medicine I, Endocrinology and Diabetes Unit, University of Wuerzburg, Wuerzburg, Germany; 2Department of Nuclear Medicine, University of Wuerzburg, Wuerzburg, Germany; 3Medical Clinic, University Hospital Innenstadt, Ludwig Maximilians University, Munich, Germany; 4Klinische Endokrinologie, Charité Campus Mitte, Charite Universitätsmedizin Berlin, Berlin, Germany.

Subject: Adrenal tumours (AT) are often detected incidentally and represent a variety of differential diagnoses with variable therapeutic consequences. We have recently developed [123I]Iodometomidate ([123I]IMTO), that specifically binds to adrenal CYP11B enzymes as a SPECT tracer for adrenal scintigraphy. This radiotracer is now evaluated in patients with adrenal tumours in an ongoing clinical trial. The study was approved by the ethical committee and patients gave written informed consent.

Methods: Patients (27 adrenocortical carcinomas (ACC), 12 adrenal adenomas (2 Conn adenomas, 3 overt Cushing adenomas, 3 subclinical Cushing adenomas, 4 nonfunctioning adenomas), 1 renal cell carcinoma and 2 metastases) received 185 MBq [123I]Iodometomidate i.v.. Biodistribution and pharmacokinetics of the tracer were studied by planar scintigraphy, SPECT and SPECT/CT over 24 h.

Results: [123I]Iodometomidat proved to be a tracer that specifically accumulates in adrenocortical tissue. Benign adrenal tumours of known adrenocortical origin were excellently visualized in SPECT/CT after 4–6 h with optimal target to background ratios after 24 h p.i. In contrast, adrenal tumours of known non-adrenocortical origin did not show any tracer uptake. Tracer uptake in patients with ACC was heterogeneous. In several patients only in the early phases a moderate tracer uptake was seen in lesions known from CT, particularly in patients with poorly differentiated tumours and patients receiving mitotane. In contrast, hormone producing ACCs exhibited high and lasting tracer uptake.

Conclusion: Due to its highly specific uptake in adrenocortical tissue [123I]IMTO is a promising tracer for noninvasive differentiation of adrenal lesions. In patients with ACC tracer uptake shows interindividual variation dependent on differentiation status and pretreatment. In ACC patients with high tracer uptake radiotherapy with [131I]Iodometomidate may hold therapeutic potential.