Peptide therapy (peptide receptor-mediated radiotherapy – PRRT) is an in-patient nuclear medicine treatment for patients with metastatic neuroendocrine tumors. Research peptides are widely available for experts to study to find new treatments. Some are already being used to treat some diseases. Here is an example of how peptides can help.
How does the principle of peptide therapy work?
Neuroendocrine tumors, well-differentiated neuroendocrine carcinomas, and their metastases have somatostatin receptors on their surface. Somatostatin analogs bind to these structures. These can be used both for diagnosis and for therapy by binding radioactive tracers to them. As a result, the radiation can be brought directly to the metastases. Therefore a specific fight against the cancer cells can take place without any relevant side effects occurring. For which diseases is peptide therapy suitable? Metastatic neuroendocrine tumors and well-differentiated neuroendocrine carcinomas with sufficient somatostatin receptors.
Which alternative therapy methods are available?
As a rule, peptide therapy is only used when the standard therapy according to the guidelines (surgery, somatostatin analogs, chemotherapy) has been exhausted and the disease still progresses.
What are the requirements for peptide therapy and what preliminary examinations are necessary?
In an interdisciplinary tumor board, the indication to carry out peptide therapy is given and an application for reimbursement is made to the health insurance company.
- Detailed anamnesis of previous and ongoing therapies, especially therapy with depot somatostatin.
- Determination of the somatostatin receptor stock with 99mTc-labeled somatostatin analog and/or 68Ga-DOTA-PET / CT.
- Laboratory tests – v. a. Blood count parameters for estimating the bone marrow reserve and retention parameters.
- Kidney sequence scintigraphy to determine and monitor the progress of kidney function.
How is peptide therapy carried out?
The treatment takes place under inpatient conditions and usually lasts between 2 and 5 days. On the day of admission, there will be a laboratory check after another consultation with the doctor. The infusion program with an amino acid solution to protect the kidneys begins in the late morning, which is why a sufficiently high amount of fluids is necessary during the course. After about 1 hour, the therapeutic agent (in most cases 177Lu-somatostatin analog) is also administered into the vein within half an hour. To control the accumulation of the therapeutic agent on the tumor cells, multiple full-body images are created in the stationary process. The radiation emanating from the patient is continuously monitored so that the time of discharge can be read in cooperation with the medical physicists.
What side effects are possible?
As part of the amino acid infusion, temporary malaise and nausea can occur. But this can be treated very well with medication or even avoided with prophylactic administration. In the first few weeks after therapy, the blood count parameters can worsen somewhat and a fatigue syndrome can occur. By using a 177Lu-somatostatin analog as a therapeutic agent, the risk of relevant kidney damage in the course is not likely.
What successes can be expected?
The peptide therapy used in otherwise “exhausted” patients generally does not lead to a cure, even if complete remissions can occasionally be achieved. In 70% of the cases, there is a reduction in symptoms and a measurable reduction in the size of the tumor manifestations can be achieved in 30% of the cases. This leads to an extension of the so-called progression-free survival (NETTER 1 Trial).
What happens after the therapy?
After discharge, regular outpatient laboratory checks should be carried out in the first few weeks. Sandostatin therapy can be resumed between courses of therapy. According to the guidelines, the therapy can be repeated 5 times at an interval of approximately 12 weeks if only 177Lu-somatostatin analog is used. An outpatient check of kidney function (sequential scintigraphy) is carried out before each new cycle. In addition, the response to treatment should be checked at regular intervals with regular re-staging examinations.