Prognostic value of total tumor volume with 68Ga DOTATOC PET/CT in predicting response to 177-Lu-DOTATOC treatment in metastatic well-differentiated neuroendocrine tumors (NETs)

e16248 Background: PET/CT with somatostatin analogues (68 Ga DOTATOC) is essential for decision-making prior to treatment with [177Lu–Dota0–Tyr3]–Octreotate (177Lu-DOTATOC), there are biological characteristics in this type of neoplasms that allow predicting the response to therapy, the tumor burden is one of the most important variables, however its estimation with conventional imaging tools is limited, currently there are reconstruction algorithms based on artificial intelligence that allow estimating the tumor burden using molecular imaging studies with 68 Ga DOTATOC, aim of this work is to determine the value of the total tumor load with this radiotracer as a predictor of overall survival in patients treated with 177Lu DOTATOC. Methods: 45 patients (11 men and 34 women) with an average age of 57.2 (range 47.2 to 66.5) with histopathological and immunohistochemical diagnosis of well-differentiated neuroendocrine tumors (NETs) in the period from 2015 to 2021 who received therapy with (177Lu-DOTATOC) and who had a baseline 68Ga DOTATOC PET to calculate total tumor volume (TVV) and semiquantitative uptake values were retrospectively included. Results: The mean follow-up was 29.3 +/- 6 months. Using ROC curves, a cut-off point of 100 cm3 was determined to differentiate responding and non-responding patients. The difference in the overall survival curves between both groups was statistically significant (470 days vs. 180 days) with p=0.07. The main sites of origin of the primary tumor were pancreas (n=24), lung (n=11), small intestine (n=7) and liver (n=3). The mean tumor volume was 305.8 cm3 (+/- 272). The organs with the highest uptake values were pancreas with SUVmax of 27.9 (range 10.1-42.4), rectum with SUVmax 26.5 (10.7-42.3) and liver with SUVmax of 22.1 (14.4-31.7), these uptake values did not have any type of relation to patient survival. Regarding therapy with 177 Lu DOTATOC, 8 received 14.8 Gbq (400mCi), 12; 22.2 GBq (600mCi) and 25; 29.6 GBq (800 mCi), no serious adverse effect or kidney function impairment was demonstrated after 177Lu DOTATOC therapy. No grade 3 or 4 haematological toxicity was identified. Conclusions: PET/CT with 68 Ga-DOTATOC is routinely used in the management of patients with neuroendocrine tumors and also allows categorizing patients according to their tumor volume to predict overall survival in patients treated with 177 Lu-DOTATOC, thus in such a way that it could be considered as an easily accessible and widely available prognostic imaging biomarker.