BRAF p.V600 mutation detection recently became necessary to treat metastatic melanoma patients with vemurafenib. This study compares different methods of detection of BRAF mutations. Melanoma samples from 111 patients were analyzed for BRAF mutations, and for 89 of them, results were obtained with the four following methods: Sanger sequencing, real-time PCR, immunohistochemistry, and pyrosequencing. All samples contained at least 60% of tumor cells. Directional Sanger sequencing of PCR products failed to detect 3 of 40 p.V600E-mutated cases (7.5%) (sensitivity, 92.5%; 95% CI, 78.5% to 98.0%). BRAF p.V600E-specific real-time PCR identified 39 of 40 p.V600E-mutated cases (97.6%) (sensitivity, 97.5%; 95% CI, 87.1% to 99.6%) and all 39 wild-type (WT) cases and surprisingly was also positive for 6/6 p.V600K (specificity, 87.8%; 95% CI, 75.8% to 94.3%). However, other mutations, p.V600R (n = 1), p.K601E (n = 2), and p.600_601delinsE (n = 1), were not detected. Immunohistochemistry with VE1, specific for p.V600E, identified all p.V600E and WT cases (sensitivity, 100%; 95% CI, 91.2% to 100%) but was negative for all other BRAF mutations. Pyrosequencing successfully identified all WT and mutated cases. Immunohistochemistry is highly specific for p.V600E, and could be used as a first-line method, as is currently performed for HER2 amplification detection. Pyrosequencing proved to be the most efficient method to detect BRAF mutations in melanomas and could be performed on VE1-negative or uninterpretable cases.

Langerhans cell histiocytosis (LCH) and the non-LCH neoplasm Erdheim-Chester disease (ECD) are heterogeneous neoplastic disorders marked by infiltration of pathologic macrophage-, dendritic cell-, or monocyte-derived cells in tissues driven by recurrent mutations activating MAPK signaling. Although recent data indicate that at least a proportion of LCH and ECD patients have detectable activating kinase mutations in circulating hematopoietic cells and bone marrow-based hematopoietic progenitors, functional evidence of the cell of origin of histiocytosis from actual patient materials has long been elusive. Here, we provide evidence for mutations in MAPK signaling intermediates in CD34 cells from patients with ECD and LCH/ECD, including detection of shared origin of LCH and acute myelomonocytic leukemia driven by -mutant CD34 cell progenitors in one patient. We also demonstrate functional self-renewal capacity for CD34 cells to drive the development of histiocytosis in xenotransplantation assays in vivo. These data indicate that the cell of origin of at least a proportion of patients with systemic histiocytoses resides in hematopoietic progenitor cells prior to committed monocyte/macrophage or dendritic cell differentiation and provide the first example of a patient-derived xenotransplantation model for a human histiocytic neoplasm.

The BRAF mutation is reported in half of patients with Langerhans cell histiocytosis (LCH). This study investigated the detection of the BRAF allele in circulating cell-free (ccf) DNA in a paediatric LCH cohort. Children with BRAF -mutated LCH were investigated to detect ccf BRAF at diagnosis (n = 48) and during follow-up (n = 17) using a picolitre-droplet digital PCR assay. At diagnosis, ccf BRAF was positive in 15/15 (100%) patients with risk-organ positive multisystem (RO+ MS) LCH, 5/12 (42%) of patients with RO- MS LCH and 3/21 (14%) patients with single-system (SS) LCH (P < 0·001, Fisher's exact test). The positive BRAF load was higher for RO+ patients (mean, 2·90%; range, 0·04-11·4%) than for RO- patients (mean, 0·16%; range, 0·01-0·39) (P = 0·003, Mann-Whitney U test). After first-line vinblastine-steroid induction therapy, 7/7 (100%) of the non-responders remained positive for ccf BRAF compared to 2/4 (50%) of the partial-responders and 0/4 of the complete responders (P = 0·002, Fisher's exact test). Six children treated with vemurafenib showed a clinical response that was associated with a decrease in the ccf BRAF load at day 15. Thus, ccf BRAF is a promising biomarker for monitoring the response to therapy for children with RO+ MS LCH or RO- LCH resistant to first-line chemotherapy.