Activating BRAF V600E Mutation in Aggressive Pediatric Langerhans Cell Histiocytosis

Abstract

Langerhans cell histiocytosis (LCH) is a rare neoplastic disease originating from cells characterized by antigen-presenting Langerhans cell phenotype. The clinical spectrum of LCH is highly variable including localized and disseminated forms mostly occurring in children. Recently, about 60% of LCHs were reported to carry the activating BRAF mutation V600E. In our retrospective study, we evaluated the occurrence and prognostic impact of the V600E mutation in formaldehyde-fixed, paraffin-embedded samples from 15 pediatric LCH cases treated at our institution. Allele-specific polymerase chain reaction (PCR) and direct sequencing were used to demonstrate the presence of V600E mutation, and immunohistochemistry (IHC) using the mutant protein-specific VE1 antibody clone was performed to confirm mutant BRAF protein expression. Eight of 15 (53.3%) cases proved to be BRAF mutants by any of the methods applied, with a single case showing a discrepancy (PCR negative/IHC positive). Four of the BRAF-mutant cases (50.0%) showed refractory disease and progressed to death within 43 months, whereas the remaining mutant cases were stable and responded well to therapy. Wild-type BRAF cases (7/15, 46.6%) with generally comparable initial presentation were all treated successfully. In conclusion, activating V600E BRAF mutation can be frequently demonstrated in pediatric LCH by both allele-specific PCR and IHC. Unfavorable risk cases potentially also responding to BRAF-inhibitory therapy can be identified by mutation testing using archival formaldehyde-fixed, paraffin-embedded tumor samples.

An immunohistochemical and genetic study of BRAFV600E mutation in Japanese patients with ameloblastoma

“…Additionally, small neoplastic foci might be insufficient to detect by PCR. This is similar to the reported false negativity of a PCR reaction caused by low tumor cell quantities in the presence of sporadic tumor cells within massive nonneoplastic tissues 24 . It was also speculated to result from mutations in proteins that share similar epitopes, such as ARAF or CRAF 22 …”

Multisystemic Pediatric Langerhans cell histiocytosis: a comprehensive clinico-pathological and BRAF V600E mutation study at autopsy

“…Recently, this mutation has been proposed to be associated with the most aggressive forms of LCH. 5,12,31 Our finding is surprising, as all our cases had multisystemic involvement with a fatal outcome. However, it has also been reported that Asian patients with LCH tend to show a lower rate of BRAF V600E mutation with a frequency ranging from 20-24% in different studies.…”

Immunohistochemistry in dermatopathology and its relevance in clinical practice

“…When present, it denotes an aggressive behavior and treatment refractoriness. [ 54 55 ] Juvenile xanthogranuloma (JXG) and reticulohistiocytomas are other histiocytic disorders commonly affecting skin. The tumor cells express CD68, alpha1 antitrypsin, alpha 1 antichymotrypsin, and factor XIII, but they are negative for LCH markers like CD1a, S-100, and Langerin [Figure 5d – f ].…”