Abstract


Introduction
The human epidermal growth factor receptor 2 (HER2) status is important for HER2 targeting therapies. T his information is obtained through immunohistochemistry (IHC) or in situ hybridisation (ISH), which necessitates tissue sampling, and may miss tumor heterogeneity as not every lesion consists of the same cells, nor expresses the same levels of HER2. To assess multiple lesions, whole-body imaging using PET/CT imaging might be a solution. A 68Ga-labeled, NOTA-coupled, single-domain antibody (sdAb) targeting the HER2 receptor has been developed (1).
Methods
In this phase II trial, 20 patients (pts) with locally advanced or metastatic breast carcinoma (BC) were included. Pts were injected intravenously with a typical dose of 100 ug and an activity range of 98-168 MBq 68GaNOTA-anti-HER2 sdAb, followed by PET/CT (Siemens Biograph Vision, 120 s per bed position and 40 s for the legs) at 90 min post injection (pi). A 2nd tracer injection, followed by PET/CT with identical parameters, was done within 8 days. In both image data sets, up to 5 lesions (minimal diameter 12mm, for lymph nodes in the short axis) per pt were selected with no more than 2 per organ system. Peak Standard Uptake Values (SUVpeak) of selected lesions were measured on both scans with Siemens' Syngo.via VB40 and compared with student t-test and Bland-Altman Plots for differences.
Results/Discussion
Out of 20 pts included with BC (6 HER2+, 14 HER2-) with a mean age of 58.6 y (37-81), three were scanned only once: one owing to the COVID-19 pandemic and two due to withdrawal of consent. An example of repeated tracer injection and subsequent imaging is shown in fig. 1. No safety concerns were identified in these 20 patients, confirming the excellent safety of this imaging tracer.
For repeatability analysis, 50 lesions were delineated by a study team member on both scans in 17 pts. No significant differences between the two measurements were found (p:0.40). The repeatability coefficient (RC) was 38.2%. The mean absolute percentage difference (MAPD), which is the mean of 1100x(SUV2- all subjects, was 13.6%, comparable to repeated values reported for 18F-FDG (2). Bland-Altman plot with the relative difference is shown in
Fig. 2. Independent uptake analysis of all lesions by a central image reviewer, blinded to the HER2 status of the patient is ongoing.
Conclusions
This study confirms that on PET/CT imaging in patients with breast carcinoma, SUVpeak is a highly repeatable metric for quantifying 68GaNOTA-anti-HER2 sdAb uptake in subsequent scans. lts repeatability is similar to that reported for other routinely used tracers, such as FDG. Additional studies to define the potential clinical benefit of this technique are currently ongoing.
Original languageEnglish
Publication statusPublished - Mar 2022
EventEMIM 2022: 17th European Molecular Imaging Meeting - Helexpo Thessaloniki, Greece, Thessaloniki, Greece
Duration: 15 Mar 202218 Mar 2022
https://e-smi.eu/meetings/emim/emim-2022/

Conference

ConferenceEMIM 2022
Country/TerritoryGreece
CityThessaloniki
Period15/03/2218/03/22
Internet address

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