BRAF p.V600E-Negative Langerhans Cell Histiocytosis Associated with a Periapical Cyst: A Case Presentation with Broad Review of the Differential Diagnosis and Disease Pathophysiology.

Abstract

Background: Langerhans cell histiocytosis (LCH) rarely presents in the oral and maxillofacial region, and while isolated and small collections of Langerhans-type cells have been found in periapical cysts, there have been no reported cases of LCH arising in periapical cysts.

Methods: A 58-year-old female presented with isolated erythematous dry skin lesions and a radiolucent lesion of the anterior maxilla. Microscopic examination of the enucleation specimen revealed a periapical cyst with large collections of atypical cells with grooved folded nuclei with eosinophils consistent with LCH. Immunohistochemistry (IHC) was performed to confirm the diagnosis. BRAF mutation status was evaluated with the BRAF p. V600E antibody and the automated real-time PCR-based Idylla™ assay, capable of qualitative detection of 5 mutations in codon 600 of the BRAF gene.

Results: The LCH cells were positive for S100, CD1a, and Langerin (CD 207) and negative for BRAF p. V600E mutations. Ki-67 was 45%.

Conclusion: The association of LCH with a periapical cyst could be explained by the active surveillance and migration of neoplastic Langerhans-type cells in blood to the site of apical chronic inflammation, in a patient with LCH. Careful attention to morphologic features in conjunction with Langerin IHC, helps exclude other closely-related dendritic tumours. BRAF p. V600E testing, ideally with real-time PCR assays, can help identify patients who may benefit from BRAF inhibitor therapies. New generations of sequencing that cover a large panel of genetic alterations beyond the frequent BRAF p. V600E mutations (e.g. rare in-frame BRAF deletions), could provide valuable information about the extent, prognosis and treatment of LCH patients.