Treatment options for unresectable neuroendocrine liver metastases

Hepatic metastases develop in 85% of patients with gastroenteropancreatic neuroendocrine tumors. Radical surgery, which involves resection of the primary and liver metastases, is the mainstay of treatment, with 60-70% 5-year survival and 35% 10-year survival rates. However, less than 15% of neuroendocrine tumor liver metastases (NETLMs) are resectable, owing either to multifocality or the inability to preserve sufficient parenchyma following resection. This article deals with the therapeutic modalities available for nonresectable liver metastases, and the therapeutic options available for management of nonresectable NETLMs are discussed. Targeted therapies for NETLMs include hepatic artery embolization, transcatheter arterial chemoembolization, radiolabeled/drug-eluting microspheres, radiofrequency ablation, cryoablation and phenol injection. Hepatic artery embolization/transcatheter arterial chemoembolization is associated with 75-100% symptom relief and an objective tumor response varying from 33 to 80%. Other modalities, such as biotherapy, peptide receptor therapy and chemotherapy, target both the primary and metastatic disease. Their effects on NETLMs as a subgroup have not been evaluated. Various therapeutic options are available for the treatment of unresectable NETLMs. Most offer significant symptomatic relief, with only a few comparative studies showing survival benefit. Most of the available evidence is based on retrospective and prospective case series rather than randomized controlled trials. Well-designed studies on existing treatment modalities and the search for newer therapeutic options are required.

Relevance of angiogenesis in neuroendocrine tumors

While traditional cytotoxic drugs have shown limited efficacy in neuroendocrine tumors (NETs), their biological features have been characterized and can be exploited therapeutically. Their most prominent trait is an extraordinary vascularization in low-grade NETs and an hypoxia-dependent angiogenesis in high-grade NETs, which is associated to a significant expression of many proangiogenic molecules. Therefore, several antiangiogenic compounds have been tested in these malignancies, and among these, sunitinib has demonstrated activity in pancreatic NET patients by dually targeting the VEGFR and PDGFR pathways. In spite of these efficacious clinical results, apparent resistance to antiangiogenic therapies has been described in NET animal models and in clinical trials. Therefore, overcoming antiangiogenic resistance is a crucial step in the subsequent development of antiangiogenic therapies. Several strategies have been postulated to fight resistance, but preclinical studies and clinical trials will investigate and address these therapeutic approaches in the coming years in order to overcome resistance to antiangiogenic therapies in NETs.

Novel medical therapies of recurrent and metastatic gastroenteropancreatic neuroendocrine tumors

Neuroendocrine tumors (NETs) of the gastrointestinal tract and pancreas are slow-growing but commonly advanced malignancies with increasing incidence and prevalence. While locoregional disease can be effectively managed with resection, treatment of recurrent, progressive or metastatic disease has until recently been limited to palliative embolization and cytoreducitve surgery, with cytotoxic chemotherapeutic agents being the last resort. However, novel molecular targeted therapies inhibiting malignant cell proliferation and neoangiogenesis, as well as new cytotoxic chemotherapy drugs and somatostatin analogues, are all being investigated for their potential use in advanced neuroendocrine tumors. Long-acting release forms of octreotide have been shown to not only improve symptoms in carcinoid syndrome but to also delay progression of gastrointestinal NETs. On the other hand, phase III trials have demonstrated everolimus (with octreotide) and sunitinib to increase progression-free survival in pancreatic NETs. Use of bevacizumab has also shown promise in a phase II study, and results of an ongoing phase III trial comparing it to interferon are eagerly expected. Use of radiolabeled somatostatin analogues is still under investigation, though several phase II studies are encouraging. New cytotoxic agents, most notably temozolomide and capecitabine, are already in use, but their relative effectiveness compared to streptozocin in pancreatic NETs is yet to be determined.

The role of angiogenesis in neuroendocrine tumors

The first studies to assess in vitro angiogenesis in neuroendocrine tumors used animal-based assays to study the antiangiogenic properties of somatostatin analogs. Current technologies enable investigators to directly appraise the in vitro angiogenic response of an individual's neuroendocrine tumor with and without potential antiangiogenic reagents. This article describes the evolution of methods to assess in vitro angiogenesis in neuroendocrine tumors and describes some of the clinical data.

Review article: future therapies for management of metastatic gastroenteropancreatic neuroendocrine tumours

BACKGROUND

Gastroenteropancreatic neuroendocrine tumours (GEP NETs) are relatively uncommon tumours that occur anywhere within the gastrointestinal tract. The prevalence of GEP NETs is estimated to be 35 per 100 000 population. Patients often present with metastatic disease and consequently, palliative treatments form the mainstay of therapy.

AIM

To review the current and novel therapeutic options for management of GEP NETs.

METHODS

Searches for all studies related to GEP NETs, NETs and carcinoid tumours in Medline and abstracts from international meetings.

RESULTS

Somatostatin analogues remain the first line therapy for management of symptoms of GEP NETs and may have anti-proliferative action. New somatostatin analogues with different somatostatin receptor affinity have been developed. Radionuclide peptide receptor therapy is established in patients with positive somatostatin scintigraphy. A number of new agents and targeted therapies are currently being evaluated in a phase I and II studies and these include angiogenic inhibitors, mammalian target of rapamycin inhibitors and immune therapies.

CONCLUSIONS

A number of nonsurgical therapies are available for management of gastroenteropancreatic neuroendocrine tumours. It is hoped, the development of some of these promising novel therapies will expand the therapeutic armamentarium.

Rationale and evidence for sunitinib in the treatment of malignant paraganglioma/pheochromocytoma

CONTEXT

Paragangliomas are tumors that develop from extraadrenal chromaffin cells. Approximately 20% of paragangliomas are malignant, and surgical resection is considered the primary treatment when possible. The optimal systemic treatment for advanced disease is undefined, due in part to lack of effective agents. Here we report our experience suggesting that sunitinib is an effective agent in this malignancy.

SETTING AND PATIENTS

Three patients with metastatic paraganglioma were treated with sunitinib at the Princess Margaret Hospital. Limited analyses of tumor tissue and germline DNA were available.

INTERVENTION

Sunitinib at a standard dose (50 mg daily, 4 wk on, 2 wk off) was titrated to patient tolerance.

RESULTS

One patient has achieved a near complete response, and two patients demonstrated partial responses. Two patients demonstrated germline defects suggesting a pseudo-hypoxic drive to the tumor whereas the third demonstrated immunohistochemical evidence of this phenomenon.

CONCLUSIONS

Sunitinib appears to be an active agent in this malignancy based on this limited cohort, with an understandable mechanism of action similar to that described in other hypoxia-driven tumors. A single arm phase 2 trial is underway.