Effect of vemurafenib on disease and BRAF V600E levels. (A) Percentage of the BRAF V600E allele in the peripheral blood of patients at time of relapse (patient 107) or diagnosis (5 other patients). Patient 107 is the patient described in this case report; patients 113 and 134 had MS-LCH, patients 103 and 216 had multifocal bone LCH, and peripheral blood of patient 151 was used as a negative control (no BRAF V600E mutation in lesional cells). (B) Immunohistochemistry of a biopsy (gingiva) of patient 107 with an antibody against V600E. Original magnification ×40. (C) Monitoring of laboratory parameters under vemurafenib. (D) Vemurafenib dosage (milligrams per day) administered to the patient. (E) Disease activity score (DAS) during treatment with vemurafenib until HSCT (see also supplemental Table 1). (F) Percentage of circulating BRAF V600E alleles in the peripheral blood (whole blood) during therapy.