Treating Metastases Associated With Neuroendocrine Tumors (NETs)

There are several treatment options available for patients with neuroendocrine tumors (NETs). An important feature of NETs is that they often metastasize to the liver, says Matthew H. Kulke, MD, and the liver may remain as the main site or only site of metastasis. Liver-directed therapy approaches, such as radio frequency ablation or irreversible electroporation, may be used for patients with a limited number of metastases that are not too large, comments Jonathan R. Strosberg, MD. Other patients may be surgical candidates for hepatic resection. In multiple liver metastases, hepatic artery embolization can interrupt blood supply from the tumor, reducing tumor growth and improving patient symptoms.

Different techniques of embolization include bland embolization, chemoembolization, and radioembolization. Bland embolization refers to embolization of microparticles with the goal of arresting blood flow from hepatic and arterial circulation to the tumors. Chemoembolization utilizes cytotoxic impregnated beads. Radioembolization may refer to resin or glass radioactive microspheres. Short-term toxicities can occur with radioembolization, including liver fibrosis, which can eventually lead to cirrhosis. In general, the short-term toxicities occur less frequently with radioembolism compared with bland embolization, notes Strosberg.

Peptide receptor radiotherapy is a relatively novel form of treatment for NETs that express somatostatin receptors, states Strosberg. This strategy directly targets tumors with radioactive isotopes attached to a somatostatin analog that are then delivered to the somatostatin receptor—expressing tumor. The most recent generation isotope, lutetium-177, improves response rates and progression-free survival and rarely results in bone marrow toxicity or nephrotoxicity, says Strosberg.

Systemic therapy is typically preferred in patients with metastasis outside of the liver, states Kulke. Although other sites of metastasis are less common, metastasis to the bone may occur and is associated with a poor outcome, says James C. Yao, MD. External beam radiotherapy may help manage focal problems, while a bone-protecting agent, such as zoledronate, can be applied in multifocal bony metastasis.