Theranostics in neuroendocrine tumours: somatostatin receptor imaging and therapy

Abstract

Theranostics and its principles: pre-treatment selection of patients who are most likely to benefit from treatment by the use of a related, specific diagnostic test are integral to the treatment of patients with neuroendocrine tumours (NETs). This is due to NETs' important, but variable, somatostatin receptor (SSTR) expression, their heterogeneity and variation in site of primary and rate of progression. Only patients whose tumours have sufficient expression of SSTRs will benefit from SSTR-based radionuclide therapy and demonstrating this expression prior to therapy is essential. This article provides a relevant overview of NETs and the multiple facets of SSTR based theranostics, including imaging and therapy radionuclides; clinical efficacy and toxicity; patient selection and treatment and finally emerging radiopharmaceuticals and newer clinical applications.

Figure 1.

A 64-year-old patient with G2 metastatic midgut NET who underwent staging with ¹⁸F-FDG and ⁶⁸Ga-DOTATATE. The ⁶⁸Ga-DOTATATE demonstrated multiple sites of avid disease within a mesenteric mass, abdominal nodes, liver and skeletal deposits. All of these lesions were not avid on ¹⁸F-FDG. ¹⁸-fludeoxyglucose; NETs, neuro endocrine tumours.

Figure 2.

A 72-year-old gentleman with G2 pancreatic NET who had PD on CT, underwent staging with ¹⁸F-FDG (a) and ⁶⁸Ga-DOTATATE (b), consideration for PRRT. There are several tracer avid liver metastases. The yellow arrows demonstrate two lesions that are DOTATATE avid and to a lesser degree FDG avid. The three red arrows demonstrate lesions that are FDG avid but ⁶⁸Ga negative. As this patient has discordant disease that is progressive, he is not suitable for PRRT. ¹⁸-fludeoxyglucose; NETs, neuroendocrine tumours; PRRT, peptide receptor radionuclide therapy.

Figure 3.

A 71-year-old male with midgut NET, small bowel resection, had pre-therapy ⁶⁸Ga-DOTATATE (a) and post-therapy ¹⁷⁷Lu-DOTATATE (b) imaging, demonstrating similar tracer distribution with avid liver and mesenteric node. NETs, neuro endocrine tumours.

Figure 4.

A 67-year-old gentleman who had four cycles of ¹⁷⁷Lu-DOTATATE imaging. Pre-therapy ⁶⁸Ga-DOTATATE (a) imaging demonstrates multiple sites of tracer avid disease in the liver. Post-therapy ⁶⁸Ga-DOTATATE imaging (b) shows an excellent response to treatment with significant reduction in size and avidity in multiple lesions (including a target lesion shown).