Antibody formation against somatostatin analogues with altered biodistribution and dosimetry: a case with implications for PRRT

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Introduction: Peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs) has emerged as a powerful palliative therapy. I.v. administration of radiolabeled (e.g. Yttrium-90) somatostatin analogues (SA) results in high-dose local irradiation of all tumor sites. The radiolabelled SA accumulates in the tumors through receptor-mediated internalization depending on the expression of somatostatin receptors and the pharmacokinetics of the radiolabelled SA.

Aim(s): Antibody formation in patients treated with SA is extremely rare and has, until now, only been described in four cases. Antibody formation after PRRT with radiolabelled SA has never been documented. We present a patient with an impressive change in biodistribution on 68Ga-DOTATOC PET/CT images performed after a first administration of 90Y-DOTATOC, most likely due to antibody formation against the SA.

Materials and methods: A 38-year-old female patient, diagnosed with a NET of the small intestine with lymph node and liver metastases and progressive under cold SA, was included in a 90Y-DOTATOC study protocol (four cycles of 1.85 GBq/m² 90Y-DOTATOC). Pretherapeutic dosimetry with 111In-octreotide scintigraphy and baseline 68Ga-DOTATOC PET/CT showed no apparent abnormalities. Seven weeks after the first cycle, a 68Ga-DOTATOC PET/CT was performed to evaluate early treatment response.

Conference: 7th Annual ENETSConcerence (2010)

Presenting Author: VAN BINNEBEEK S

Authors: Van Binnebeek S, DeRoose C, Van Billoen B, Baete K, Mortelmans L,

Keywords: antibody, somatostatin analogue, 90Y-DOTATOC, dosimetry, PRRT, 68Ga-DOTATOC,