Dramatic response to encorafenib in a patient with Erdheim-Chester disease harboring the BRAFV600E mutation

Efficacy of Combined Encorafenib and Binimetinib Treatment for Erdheim-Chester Disease Harboring Concurrent BRAFV600E and KRASG12R Mutations: A Case Report

BACKGROUND

Erdheim-Chester disease (ECD) is a rare form of non-Langerhans cell histiocytosis with diverse clinical manifestations, often associated with mutations in the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway. BRAF and KRAS mutations, which are driver mutations of oncogenes, participate in the same signaling pathway (MAPK/ERK pathway) and are usually mutually exclusive. We report a case of ECD with concurrent BRAFV600E and KRASG12R mutations treated using BRAF and MEK inhibitors.

CASE

A 70-year-old man was referred to our hospital with a mesenteric nodal lesion on computed tomography scan. The patient experienced symptoms consistent with ECD, including central diabetes insipidus. Biopsy revealed histiocytes positive for CD68 and CD163, negative for S100, CD1a, and CD21. Liquid-based comprehensive genomic profiling and tissue-based cancer gene panel test identified BRAFV600E and KRASG12R mutations with different variant allele fraction. Additional immunohistochemistry with an antibody specific to mutant BRAFV600E protein stained some proliferating histiocytes, consistent with ECD. Based on the genomic profiling results, we hypothesized that there was a coexistence of a clone harboring BRAFV600E and another clone harboring KRASG12R, and planned a combination therapy with BRAF and MEK inhibitors targeting each clone, respectively. The patient received oral encorafenib at 100 mg once daily and oral binimetinib at 15 mg twice daily. The combination therapy resulted in rapid resolution of symptoms and significant improvement in imaging findings.

CONCLUSION

This case represents a unique presentation of ECD with concurrent BRAFV600E and KRASG12R mutations. Combination therapy with encorafenib and binimetinib targeting each clone resulted in a remarkable therapeutic effect and was well-tolerated. This is the first reported case of ECD treated with encorafenib and binimetinib. The combination therapy with BRAF and MEK inhibitors is one of the rational treatment options for cases of ECD with a suspicion of multiple clones.

Current State of Targeted Therapy in Adult Langerhans Cell Histiocytosis and Erdheim-Chester Disease

The mitogen-activated protein kinase (MAPK) pathway is a key driver in many histiocytic disorders, including Langerhans cell histiocytosis (LCH) and Erdheim-Chester disease (ECD). This has led to successful and promising treatment with targeted therapies, including BRAF inhibitors and MEK inhibitors. Additional novel inhibitors have also demonstrated encouraging results. Nevertheless, there are several problems concerning targeted therapy that need to be addressed. These include, among others, incomplete responsiveness and the emergence of resistance to BRAF inhibition as observed in other BRAF-mutant malignancies. Drug resistance and relapse after treatment interruption remain problems with current targeted therapies. Targeted therapy does not seem to eradicate the mutated clone, leading to inevitable relapes, which is a huge challenge for the future. More fundamental research and clinical trials are needed to address these issues and to develop improved targeted therapies that can overcome resistance and achieve long-lasting remissions.

Erdheim-Chester Disease Due to a Novel Internal Duplication of NRAS: Response to Targeted Therapy with Cobimetinib

Histiocytoses encompass a group of exceptionally rare disorders characterized by the abnormal infiltration of tissues by histocytes. Among these, Erdheim-Chester disease (ECD) stands out as a multisystem histiocytosis that typically affects bones and various other tissues. Historically, the treatment of ECD has been challenging. However, recent breakthroughs in our understanding, particularly the discovery of somatic mutations in the RAS-MAPK pathway, have opened new opportunities for targeted therapy in a significant subset of patients with ECD and other histiocytoses. In this report, we present the case of a patient with ECD harboring a previously unidentified microduplication in the NRAS gene in a small fraction of skin cells. This discovery played a pivotal role in tailoring an effective therapeutic approach involving kinase inhibitors downstream of NRAS. This case underscores the crucial role of deep sequencing of tissue samples in ECD, enabling the delivery of personalized targeted therapy to patients.