Targetable BRAF and RAF1 Alterations in Advanced Pediatric Cancers

RAF family protein kinases signal through the MAPK pathway to orchestrate cellular proliferation, survival, and transformation. Identifying BRAF alterations in pediatric cancers is critically important as therapeutic agents targeting BRAF or MEK may be incorporated into the clinical management of these patients. In this study, we performed comprehensive genomic profiling on 3,633 pediatric cancer samples and identified a cohort of 221 (6.1%) cases with known or novel alterations in BRAF or RAF1 detected in extracranial solid tumors, brain tumors, or hematological malignancies. Eighty percent (176/221) of these tumors had a known-activating short variant (98, 55.7%), fusion (72, 40.9%), or insertion/deletion (6, 3.4%). Among BRAF altered cancers, the most common tumor types were brain tumors (74.4%), solid tumors (10.8%), hematological malignancies (9.1%), sarcomas (3.4%), and extracranial embryonal tumors (2.3%). RAF1 fusions containing intact RAF1 kinase domain (encoded by exons 10-17) were identified in seven tumors, including two novel fusions TMF1-RAF1 and SOX6-RAF1. Additionally, we highlight a subset of patients with brain tumor with positive clinical response to BRAF inhibitors, demonstrating the rationale for incorporating precision medicine into pediatric oncology. IMPLICATIONS FOR PRACTICE: Precision medicine has not yet gained a strong foothold in pediatric cancers. This study describes the landscape of BRAF and RAF1 genomic alterations across a diverse spectrum of pediatric cancers, primarily brain tumors, but also encompassing melanoma, sarcoma, several types of hematologic malignancy, and others. Given the availability of multiple U.S. Food and Drug Administration-approved BRAF inhibitors, identification of these alterations may assist with treatment decision making, as described here in three cases of pediatric cancer.

BRAF and MEK inhibitors in pediatric glioma: new therapeutic strategies, new toxicities

INTRODUCTION

BRAF mutation was initially reported in metastatic melanomas, and more recently in a variety of human cancers. BRAF acts as a down-stream effector of growth factor signaling leading to cell cycle progression, proliferation and survival. Development of selective inhibitors of BRAF has improved the survival of patients with melanoma and offers potential new therapeutic strategy in children with BRAF-mutant glioma. Areas covered: Mechanisms of resistance to BRAF inhibitors have recently been described as due to the paradoxical activation of the MAPK pathway. Combination therapy with BRAF and MEK inhibition has proved capable of overcoming the resistance with effective results in patients with melanoma. Prospective studies in pediatric glioma are warranted. Combination therapy has a different toxicity profile compared to BRAF inhibitor alone. Herein we review the state-of-the-art of toxicities associated with these agents, with a special focus on children. Expert opinion: Some toxicities appear more specific to adults, due to a combination of factors, such as patient age and predisposing risk factors. Moreover, it is recommended that the co-administration of BRAF inhibitors and drugs metabolized by the cytochrome P450 system in the liver be avoided, as this can lead to significant complications secondary to pharmacological interactions.

Treatment of Langerhans cell histiocytosis: role of BRAF/MAPK inhibition

Langerhans cell histiocytosis (LCH) is a clonally derived neoplasm with a highly variable clinical course. Although LCH was once considered a disorder of immune regulation, the identification of activating mutations in the proto-oncogene BRAF-V600E in ∼50%-60% of cases and MEK and ERK phosphorylation in 100% of examined cases, has changed the definition of LCH to a dendritic cell neoplasm with a strong inflammatory component. Current international LCH trials are focused on further improving the outcome of high-risk multisystem LCH patients, by decreasing the reactivation rate, optimizing early salvage regimens, and preventing late sequelae. Anecdotal responses to vemurafenib, a BRAF-V600E inhibitor, have been reported in a few cases of LCH and Erdheim–Chester disease. However, the development of resistance, as well as the potential risks of cutaneous and pancreatic cancers in patients with BRAF-V600E-mutated melanoma treated with single inhibitors, suggest the need for prospective trials with BRAF inhibitors, alone or in combination with other inhibitors of this pathway, for patients with refractory or multiply-relapsed LCH. The recent discovery of somatic mutations in ARAF and in MAP2K1, which lead to activation of the RAS-RAF-MEK –ERK pathway in the setting of wild-type BRAF, as well as the finding that activating mutation in MAP2K1 are relatively insensitive to MEK inhibitors, suggest that a more detailed understanding of this pathway in LCH may be necessary for the development of more effective targeted therapies.

Treatment of Langerhans cell histiocytosis: role of BRAF/MAPK inhibition

Langerhans cell histiocytosis (LCH) is a clonally derived neoplasm with a highly variable clinical course. Although LCH was once considered a disorder of immune regulation, the identification of activating mutations in the proto-oncogene BRAF-V600E in ∼50%-60% of cases and MEK and ERK phosphorylation in 100% of examined cases, has changed the definition of LCH to a dendritic cell neoplasm with a strong inflammatory component. Current international LCH trials are focused on further improving the outcome of high-risk multisystem LCH patients, by decreasing the reactivation rate, optimizing early salvage regimens, and preventing late sequelae. Anecdotal responses to vemurafenib, a BRAF-V600E inhibitor, have been reported in a few cases of LCH and Erdheim–Chester disease. However, the development of resistance, as well as the potential risks of cutaneous and pancreatic cancers in patients with BRAF-V600E-mutated melanoma treated with single inhibitors, suggest the need for prospective trials with BRAF inhibitors, alone or in combination with other inhibitors of this pathway, for patients with refractory or multiply-relapsed LCH. The recent discovery of somatic mutations in ARAF and in MAP2K1, which lead to activation of the RAS-RAF-MEK –ERK pathway in the setting of wild-type BRAF, as well as the finding that activating mutation in MAP2K1 are relatively insensitive to MEK inhibitors, suggest that a more detailed understanding of this pathway in LCH may be necessary for the development of more effective targeted therapies.