212P Correlation of 68Ga-SSO120 PET with SSTR2 expression and prognostic value in patients with small cell lung cancer

Positron Emission Tomography (PET) imaging of the somatostatin receptor 2 (SSTR2)-antagonist satoreotide trizoxetan (SSO120, previously OPS202) is a novel technique for accurate staging of patients with small cell lung cancer (SCLC). Here, we evaluate the prognostic value of 68Ga-SSO120 PET at initial staging of patients with SCLC and correlate uptake in PET imaging with SSTR2 expression in immunohistochemistry (IHC). We retrospectively included patients who underwent 68Ga-SSO120 PET/CT during initial diagnostic workup of SCLC. PET-positive tumor lesions were manually segmented and SUVmax/SUVpeak values were estimated. The whole-body SSTR2-expressing tumor volume (SSTR-TV) was calculated from all lesions per patient. For patients with available tumor biopsies, SSTR2 expression was assessed by IHC on a 4-level scale (0: negative, 1: 1-30%, 2: 30-70%, 3: ≥70%), which was correlated with SUVmax/SUVpeak in a lesion-based analysis. The association of SSTR-TV with overall survival (OS) was analysed by univariate Cox regression. We included 43 patients (22 female/21 male), 15 with limited and 28 with extensive disease according to VALG classification. Mean administered activity was 142 MBq and mean uptake time 63 min. For 34 patients, pathological specimens were available. Lesion SUVmax/SUVpeak significantly correlated with histopathological SSTR2-expression (Spearman's rho 0.73/0.70, p<0.001). Patients with a SSTR2-TV ≥130 mL (13 extensive, 2 limited disease, cut-off identified on data for best separation) showed a significantly shorter OS than patients with lower SSTR2-TV (15 extensive, 13 limited disease) (median OS: 10.8 vs. 16.1 mos; HR: 0.35, 95%-CI: 0.12-0.99, p=0.038). In patients with SCLC, tumor uptake in 68Ga-SSO120 PET correlates with histopathological SSTR2-expression and SSTR2-TV was associated with poorer OS. Investigation of a larger cohort is warranted to analyse other OS determinants (e.g., VALG and type of distant metastases) and to identify candidates for SSTR2-directed radionuclide therapy using 177Lu-SSO110.