Peptide Receptor Radionuclide Therapy in Patients With Neurofibromatosis Type 2: Initial Experience

[Neurofibromatosis]

BACKGROUND & FOCUS

While the Neurofibromatoses have been observed and classified by their phenotypes for several centuries, their great variability constitutes a considerable challenge in diagnostics and therapy selection. This article focuses on highlighting the three most frequent sub-types NF1, NF2 and NF3.

METHODS

All three NF types are outlined by the following measures: the history of their clinical detection, the typical appearance, the underlying genetic constitution and its consequences, the official diagnostic criteria, the mandatory diagnostic steps and finally the treatment opportunities and specific risks.

RESULTS

About 50% of NF patients have a positive family history and the other 50% are the first symptomatic generations and suffer from new mutations. A considerable (unknown) number of patients do not exhibit a complete genetic NF constitution, but have a so-called mosaic sub-form with only a limited number of cells being genetically affected and prone to tumorous changes. The neurofibromatoses are neuro-cutaneous diseases with manifestations at the skin and nervous system, except for NF 3, where the skin and eyes are never affected. Skin and eye manifestations, especially pigmentation disturbances, mostly started early in childhood and adolescence. The underlying genetic constitutions, on chromosome 17 in NF1 and on chromosome 22 in NF2 and NF3, cause a defect in tumor suppressor genes and lead to excessive proliferation of Schwann cells. Major features are tumors of the peripheral nerves, including cranial and spinal nerves leading to tumors with considerable nerve, brain and spinal cord compression and resulting in pain, sensory and motor deficits. A further variable disease feature may be neuropathy with neuropathic pain, related to tumor formation or even independent of it.Although benign by histopathology and growing rather slowly, those tumors often cause progressive neurological deficit and loss of function. Loss of function may be prevented by adequate timing of therapy such as nerve decompression by microsurgical tumor resection or reduction, medication with immunotherapy or radiotherapy in selected cases. To date it is unknown why some tumors remained silent and stable while others progress and show periods of accelerated growth.As a consequence, NF patients need to be accompanied by a specialized interdisciplinary NF team at long-term, with a clear-cut standardized protocol for clinical and imaging controls along with counseling and support in decision-making.Further, NF patients may suffer from reactive depression due to the danger of losing essential neural functions, such as vision or audition or movement. And especially NF1 patients show characteristics of ADHS and other cognitive compromise in at least 50% of cases.

CONCLUSIONS

As the neurofibromatosis belong to the so-called rare diseases, all patients with a suspicion or diagnosis of NF should get the opportunity to present to an interdisciplinary NF Center, mostly situated at University Hospitals, where competent counseling on the individual disease phenotype may be provided. Here the patients will be informed on the necessary diagnostic steps, their frequency as well as on practical steps in case of acute deterioration. Most NF centers are run by neurosurgeons or neurologists or pediatricians, working in a network with geneticists, neuro-radiologists, ophthalmologists, dermatologists, plastic and general surgeons, psychologists, psychiatrists and social work experts. They participate regularly in neuro-oncological tumor and sarcoma tumor boards, skull base tumor centers, comprehensive hearing centers, and deliver all the treatment opportunities provided by certified brain tumor centers, among those the inclusion in special diagnostic and treatment studies or the contact information to patient support groups.

The Current Role of Peptide Receptor Radionuclide Therapy in Meningiomas

Meningiomas are the most common primary intracranial tumors. The majority of patients can be cured by surgery, or tumor growth can be stabilized by radiation. However, the management of recurrent and more aggressive tumors remains difficult because no established alternative treatment options exist. Therefore, innovative therapeutic approaches are needed. Studies have shown that meningiomas express somatostatin receptors. It is well known from treating neuroendocrine tumors that peptide radioreceptor therapy that targets somatostatin receptors can be effective. As yet, this therapy has been used for treating meningiomas only within individual curative trials. However, small case series and studies have demonstrated stabilization of the disease. Therefore, we see potential for optimizing this therapeutic option through the development of new substances and specific adaptations to the different meningioma subtypes. The current review provides an overview of this topic.

Bombesin Receptor Family Activation and CNS/Neural Tumors: Review of Evidence Supporting Possible Role for Novel Targeted Therapy

G-protein-coupled receptors (GPCRs) are increasingly being considered as possible therapeutic targets in cancers. Activation of GPCR on tumors can have prominent growth effects, and GPCRs are frequently over-/ectopically expressed on tumors and thus can be used for targeted therapy. CNS/neural tumors are receiving increasing attention using this approach. Gliomas are the most frequent primary malignant brain/CNS tumor with glioblastoma having a 10-year survival <1%; neuroblastomas are the most common extracranial solid tumor in children with long-term survival<40%, and medulloblastomas are less common, but one subgroup has a 5-year survival <60%. Thus, there is an increased need for more effective treatments of these tumors. The Bombesin-receptor family (BnRs) is one of the GPCRs that are most frequently over/ectopically expressed by common tumors and is receiving particular attention as a possible therapeutic target in several tumors, particularly in prostate, breast, and lung cancer. We review in this paper evidence suggesting why a similar approach in some CNS/neural tumors (gliomas, neuroblastomas, medulloblastomas) should also be considered.