Peptide receptor radionuclide therapy as a potential tool for neoadjuvant therapy in patients with inoperable neuroendocrine tumours (NETs)

Neuroendocrine tumours (NET) are a heterogeneous group of neoplasms of diffuse neuroendocrine cells. Surgery is the main aim in the treatment of NETs, which becomes impossible in the case of large tumours or infiltration into other tissues and/or important blood vessels. Neoadjuvant therapy might be helpful in decreasing NET size also, leading us to the point where a tumour, previously considered inoperable, becomes operable. The aim of the study was to assess the usage of peptide receptor radionuclide therapy (PRRT) as a neoadjuvant treatment, enabling surgical intervention in primary inoperable NET. Among 47 patients treated with PRRT, 6 patients were chosen with large, inoperable tumours, for whom enabling of complete surgical excision of the lesions might offer the prospect for a cure. Response to the therapy was assessed according to Response Evaluation Criteria In Solid Tumors (RECIST). The mean tumour size decreased from 6.9 (min. 3.1 cm, max. 9.6 cm) before therapy to 5.4 cm (min. 3.1 cm, max. 9.5 cm) after the treatment. According to RECIST, stabilization of the disease was observed in four and partial responses in two patients. In two patients, reduction of the tumour size enabled surgical intervention. (1) PRRT might be considered a neoadjuvant therapy in primary inoperable NETs. (2) According to RECIST, stabilization of the disease was observed in the majority of patients. (3) We suggest that not only tumour diameter changes, but also tumour volume and contrast enhancement changes in computed tomography should be taken into consideration in assessment of the response to the therapy. (4) Somatostatin receptor scintigraphy is an important tool for qualification of the radioisotope therapy and also for the assessment of the response to PRRT. (orig.)