Peptide receptor radiotherapy (PRRT) as a potential tool of neoadjuvant therapy in patients with inoperable neuroendocrine tumors (NETs)

1743 Objectives Surgical eradication is the main aim in the treatment of NETs, which becomes impossible in the case of large tumors or infiltration into other tissues and/or important blood vessels. Neoadjuvant therapy might be helpful in decreasing neuroendocrine tumor’ size also. Methods Within the group of 47 patients treated with PRRT, 6 patients were chosen with large, inoperable tumors, for whom enabling of complete surgical excision of the lesions might be the prospect for a cure. There were 5 patients with foregut tumors and 1 with midgut tumor). Every patient received a dose of 7.4 GBq/m2 90Y-DOTA TATE in 4-5 cycles every 6-9 weeks. The mean dose was 13.6 GBq (min 11.1 GBq, max 14.8 GBq). Response to the therapy was assessed according to RECIST criteria. Results After the treatment, mean tumor size decreased to 6.9 cm with SD 2 cm (min 3.1 cm, max 9.6 cm). According to RECIST criteria, stabilization of the disease was observed in 4, partial responses in 2 patients. In two patients, reduction of the tumor size enabled surgical intervention. Conclusions 1. PRRT might be considered a neoadjuvant therapy in primary inoperable neuroendocrine tumors. 2. According to RECIST criteria stabilization of the disease was observed in the majority of patients. 3. We suggest that not only tumor’ diameter changes, but also tumor’ volume and contrast enhancement changes in CT should be taken into consideration in assessment of the response to the therapy