Peptide Receptor Radionuclide Therapy (PRRT)

Overview

Peptide Receptor Radionuclide Therapy (PRRT) is a kind of targeted cancer therapy designed for specific neuroendocrine tumors (NETs). This therapy targets receptors on tumor cells, delivering a precise dose of radioactivity to effectively destroy them. Although PRRT is not a cure, it can significantly slow down or stop tumor growth, improving both the length and quality of life for patients with NETs.

Types

In 2018, the first drug for PRRT was approved. Lutetium Lu 177 dotatate combines dotatate, a synthetic version of the hormone somatostatin, with the radioactive element lutetium-177. Somatostatin inhibits hormone secretion, and some neuroendocrine tumor (NET) cells have receptors that dotatate binds to.

Researchers are currently developing several peptide receptor radionuclide therapy (PRRT) drug combinations, with many undergoing clinical trials for eligible patients.

Reasons for undergoing the procedure

PRRT is currently used for treating gastroenteropancreatic neuroendocrine tumors (NETs) found in the pancreas, rectum, small and large intestines, or stomach. It is often recommended in people with specific circumstances, such as:

• Other treatments failed to improve their condition. People with neuroendocrine tumors (NETs) might use hormone therapy to stop the tumors from growing and to manage related symptoms. However, sometimes the tumors might still grow despite this treatment.
• Do not qualify for surgery. Many patients with neuroendocrine tumors already have metastases from their malignancy. The usefulness of surgery is reduced if the cancer has already metastasized or spread to other parts of the body.
• Have NETs with somatostatin receptors present. Unlike other treatments, an octreotide scan does not destroy the cancer cells but helps doctors see where the tumors are located. If someone has NETs with somatostatin receptors, an octreotide scan can detect it. This scan uses a substance that attaches to the tumor cells, allowing a PET scan to spot the tumors more easily.

Risks

Common adverse effect of PRRT include:

• Nausea and vomiting
• Developing blood cancers such as leukemia
• Low blood cell counts, which can result in shortness of breath, increased infection risk, and easy bruising
• Kidney or liver issues

People undergoing PRRT treatment undergo frequent blood tests throughout the eight-month treatment period, allowing their healthcare provider to adjust or discontinue treatment if complications arise.

PRRT has a rare but severe side effect known as carcinoid crisis. It is more common in those with carcinoid syndrome. Excess hormones secreted by the tumor cells are the source of this possibly fatal reaction.

Seek immediate medical attention if any of the carcinoid syndrome symptoms is experienced:

• Palpitations, or a racing or thumping heart
• Severe diarrhea
• Skin flushing or reddening, particularly on the face or neck
• Hypotension, or low blood pressure
• Breathing difficulties

Procedure

PRRT (Peptide Receptor Radionuclide Therapy) combines a protein that specifically binds to receptors on tumor cells with a radioactive element called a radionuclide. This process is akin to a key fitting into a lock: the protein attaches to the tumor cell, enabling the radionuclide to enter. Once inside, the radioactivity damages the DNA of the tumor cell, leading to its destruction.

By targeting specific receptors on tumor cells, PRRT delivers treatment directly to cancer cells while minimizing harm to healthy cells.

Before the procedure

To prepare for the procedure, these may be expected:

• Blood tests will be conducted one week before each PRRT session to confirm it is safe to proceed.
• Long-acting somatostatin analogs should be stopped at least 4 weeks prior, and short-acting analogs 24 hours before the treatment.
• Repeated high doses of glucocorticosteroids should be avoided during PRRT.
• Discontinue certain medications before starting PRRT treatment.

During the procedure

PRRT is typically performed as an outpatient procedure at a hospital’s nuclear medicine department or infusion center.

PRRT session lasts about five to six hours, and usually involves four treatments administered every two months over an eight-month period. One may receive medications an hour beforehand to help prevent nausea and vomiting.

The procedure is done as follows:

• An IV needle is inserted into the patient’s hand or arm to access a vein.
• Amino acids will be administered through the IV over about four hours to protect the kidneys.
• Approximately 30 minutes after starting the amino acid infusion, PRRT will be given through the IV, taking 30 to 45 minutes to complete, and continuing until the full dose of amino acids is administered.
• After the infusions are finished, the healthcare provider will remove the IV.

After the procedure

The day following PRRT, scans will be conducted to evaluate the movement of the radionuclide throughout your body.

Outcome

While PRRT can effectively shrink or stabilize tumors, leading to prolonged survival and improved quality of life for many individuals with neuroendocrine tumors (NETs), it is not a cure. Most patients will eventually see a recurrence of their tumors.

Within 48 hours after PRRT treatment, a carcinoid crisis may occur, although this is rare. It is crucial to seek immediate medical attention if you experience any symptoms, such as flushing, diarrhea, shortness of breath, or heart palpitations. Additionally, it’s important to remain vigilant for other potential complications.