Plasma-derived Cell Free DNA for the Diagnosis of Ocular-Involving Histiocytosis

Purpose: Circulating tumor DNA (ctDNA) is released into the plasma by many cancers and offers clinical applications including noninvasive diagnostics. Histiocytosis results from myelogenous clonal expansion of histiocytes, predominantly driven by mutations in the mitogen-activated protein kinase pathway that are potentially detectable by ctDNA-based sequencing assays. However, ocular-involving histiocytosis is often a diagnostic challenge leading to delayed diagnosis and the need for invasive biopsy of sensitive ocular structures. The purpose of this study is to determine whether sequencing of plasma-derived ctDNA can noninvasively diagnose ocular-involving histiocytosis. Design: Single tertiary cancer referral center. Participants: Twenty-four adult patients with ocular-involving histiocytosis and ctDNA sequencing. Methods: Circulating tumor DNA was analyzed (via digital droplet polymerase chain reaction for BRAF V600E, and/or next-generation sequencing) and variant allele frequency was measured at initial presentation to our center. Patient demographics, clinical characteristics, and oncogenic mutations identified from tumor-based sequencing were recorded. Main Outcome Measures: Plasma-derived ctDNA detectability of pertinent driver mutations of histiocytosis. Results: At the initial presentation of 14 patients with ocular-involving histiocytosis, sequencing of plasmaderived ctDNA detected driver mutations for histiocytosis (BRAF V600E [10], KRAS [2], ARAF [1], and concurrent MAP2K1/KRAS [1]). Mutations found in circulating cell-free DNA were 100% concordant in 11 of 11 patients with mutations identified by solid tumor sequencing. Of 10 patients without driver mutation detected in ctDNA, 3 patients had alterations (CBL mutation or kinase fusion) not captured in the ctDNA sequencing assay, 3 were wildtype even by tumor sequencing; in 4 patients, tumor-based sequencing identified mutations (BRAF [2], MAP2K1 [2]) not detected in ctDNA. Detectable mutations in ctDNA were significantly more likely in patients with uveal infiltration ( P 1 / 4 0.036). Conclusions: In this cohort, plasma-derived ctDNA was detectable and diagnostic in the majority of patients with ocular-involving histiocytosis. This suggests that if ocular histiocytosis is suspected (particularly if involving the uvea), noninvasive plasma-derived ctDNA analysis is a helpful diagnostic tool that may obviate the need to invasively biopsy sensitive ocular structures.