Neuroendocrine tumors (NET) are rare tumors characterized by slow and indolent tumor growth. Since patients with NET frequently present with liver metastases at the time of initial diagnosis, only a minority of patients with liver metastases of neuroendocrine tumors (NELM) are suitable for curative, surgical resection [1]. Intra-arterial liver targeted therapies, such as transarterial embolization (TAE), transarterial chemoembolization (TACE) and transarterial radioembolization (TARE), have emerged as effective treatment options and are recommended for NET with hepatic-predominant disease [2], [3], [4], [5].

TARE is a transcatheter intra-arterial procedure that is used for the treatment of primary and secondary hepatic tumors. It involves the selective delivery of microspheres impregnated with the radioisotope yttrium-90 (Y90, 90Y) to the target tumor(s) through the hepatic arterial vasculature, allowing for the safe administration of high radiation doses to the tumor [6].

However, the selection of patients who will benefit from these treatments is hindered by the large biological heterogeneity of NETs [7]. Prognostic criteria for a response to TARE primarily rely on clinical parameters such as hepatic tumor burden and the presence of extrahepatic metastases [8,9]. Yet, these prognostic factors have been predominantly studied in patients with primary hepatocellular carcinoma or colorectal carcinoma whose prognosis differs substantially from patients with NET. In addition, the prognostic value of imaging biomarkers such as apparent diffusion coefficient (ADC) in diffusion-weighted imaging (DWI) or standardized uptake value (SUV) in somatostatin receptor (SSR) positron emission tomography/computed tomography (PET/CT) has not been extensively evaluated in patients with NELM. DWI is routinely used for improved detection of liver metastasis and plays an increasing role in treatment response assessment. Several retrospective studies have shown that DWI and ADC measurements can be used to assess tumor response of liver metastases / liver tumors and even predict tumor response based on baseline ADC values [10], [11], [12], [13].

Studies have demonstrated the prognostic and predictive value of imaging parameters derived from SSR-PET/CT in patients with NET treated with peptide receptor radionuclide therapy (PRRT) or octreotide [14], [15], [16], [17]. In patients with NELM undergoing TARE, changes in SUV tumor-to-organ ratios could help identify patients with longer hepatic progression free survival (HPFS) [18]. Similarly, Filippi et al. found that a decrease in liver-to-spleen SUV ratio using 68Ga-DOTATOC PET between pre- and post-TARE examinations is associated with improved overall survival (OS) and progression-free survival (PFS) [16]. Additionally, Ingenerf et al. suggested that early percentage changes in SUV tumor-to-organ ratios on the first follow-up after TARE could serve as a prognostic marker for longer HPFS and aid in assessing therapeutic strategies [18].

To date, no studies have investigated the role of pretherapeutic DWI and PET/CT in predicting tumor response in patients with NELMs undergoing TARE. Therefore, the aim of this study was to identify prognostic clinical and imaging parameters (ADC and SUV values) in patients with NELMs treated with TARE.