Metastatic or locally advanced mediastinal neuroendocrine tumours: outcome with 177Lu-DOTATATE-based peptide receptor radionuclide therapy and assessment of prognostic factors

BACKGROUND: Primary neuroendocrine tumours (NETs) of mediastinum are unusual tumours with aggressive biological behaviour with limited treatment options and guarded prognosis. METHODS: Twenty-seven patients with histopathologically and radiologically proven metastatic or advanced mediastinal NET, who had undergone 177Lu-DOTATATE PRRT, were included in this retrospective analysis. Descriptive statistics was employed to calculate the cumulative overall survival (OS) and progression-free survival (PFS), determining correlation and strength of correlation between different variables with OS and PFS and finally, predictors of outcome (OS and PFS). RESULTS: In all 27 patients enrolled and analyzed, complete symptomatic response was observed in 10 patients (37%), partial response in seven patients (25.9%), symptomatically stable disease in four patients (14.8%), and symptoms progressed or worsened in six patients (22.2%). Metabolic response evaluation demonstrated complete metabolic response in one patient (3.7%), partial metabolic response was seen in nine patients (33.3%), metabolically stable disease was seen in five patients (18.5%), and 12 patients (44.4%) showed metabolic disease progression. None of the patients achieved complete anatomical/morphological response, six (22.2%) showed partial response, seven (25.9%) showed stable disease, and in 14 patients (51.9%), there was morphological disease progression. At the time of analysis, 10 patients (37%) succumbed to the disease. The median PFS was 36 months and the median OS was 66 months. Bivariate analysis showed significant level of association of PFS with surgical intervention, higher cumulative PRRT dose, metabolic response, smaller sized primary lesion, and low lesional FDG uptake. With regard to OS, higher cumulative PRRT dose, low FDG uptake and longer PFS showed significant association. CONCLUSION: Previous surgical intervention (including debulking surgery with R1 resection), higher cumulative dose of PRRT, and low FDG uptake of the tumour are associated with prolonged OS and PFS in patients with metastatic or advanced mediastinal NETs and were independent favourable prognostic markers.