BRAF V600E is associated with higher incidence of second cancers in adults with Langerhans cell histiocytosis.

In this retrospective study, BRAF mutation status did not correlate with disease extent or (event-free) survival in 156 adults with Langerhans cell histiocytosis. BRAFV600E was associated with an increased incidence of second malignancies, often comprising hematological cancers, which may be clonally related.

The role of etoposide in the treatment of adult patients with hemophagocytic lymphohistiocytosis.

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal inflammatory clinical condition, in which an exaggerated immune response is ineffectively regulated. Although etoposide-containing regimens are generally recommended for children with HLH, the exact role of etoposide in the adult setting remains unclear. We performed a systematic review of the literature on the use of etoposide in adults with HLH. All articles written in English on the use of etoposide in adults with HLH available from seven databases and published on or before July 2021 were analyzed. Thirteen studies were found to be relevant to the search results. Ten of these studies report a statistical analysis on the effect of etoposide, of which five found etoposide-containing regimens superior to non-etoposide-containing regimens. Seven studies provided sufficient data to be included in the meta-analysis. For these data, the estimated logit relative risk of etoposide on survival was 1.06 (95% confidence interval: 0.92-1.21, standard error: 2.06). The pooled data of the meta-analysis did thus not support a beneficial effect of etoposide. It should be taken into account that the presented results are highly susceptible to bias and that the effect of etoposide differs between HLH-triggers. Although the meta-analysis does not support the effect of etoposide, we do not recommend abandoning etoposide as treatment modality. The limitations of the meta-analysis, together with several individual articles confirming the benefit of etoposide, justify etoposide for select cases in adults with HLH such as refractory or severe disease with (threatening) multiorgan failure.

Clinicogenomic associations in childhood Langerhans cell histiocytosis: an international cohort study.

Langerhans cell histiocytosis (LCH) is a rare neoplastic disorder caused by somatic genetic alterations in hematopoietic precursor cells differentiating into CD1a+/CD207+ histiocytes. LCH clinical manifestation is highly heterogeneous. BRAF and MAP2K1 mutations account for ∼80% of genetic driver alterations in neoplastic LCH cells. However, their clinical associations remain incompletely understood. Here, we present an international clinicogenomic study of childhood LCH, investigating 377 patients genotyped for at least BRAFV600E. MAPK pathway gene alterations were detected in 300 (79.6%) patients, including 191 (50.7%) with BRAFV600E, 54 with MAP2K1 mutations, 39 with BRAF exon 12 mutations, 13 with rare BRAF alterations, and 3 with ARAF or KRAS mutations. Our results confirm that BRAFV600E associates with lower age at diagnosis and higher prevalence of multisystem LCH, high-risk disease, and skin involvement. Furthermore, BRAFV600E appeared to correlate with a higher prevalence of central nervous system (CNS)-risk bone lesions. In contrast, MAP2K1 mutations associated with a higher prevalence of single-system (SS)-bone LCH, and BRAF exon 12 deletions seemed to correlate with more lung involvement. Although BRAFV600E correlated with reduced event-free survival in the overall cohort, neither BRAF nor MAP2K1 mutations associated with event-free survival when patients were stratified by disease extent. Thus, the correlation of BRAFV600E with inferior clinical outcome is (primarily) driven by its association with disease extents known for high rates of progression or relapse, including multisystem LCH. These findings advance our understanding of factors underlying the remarkable clinical heterogeneity of LCH but also question the independent prognostic value of lesional BRAFV600E status.

Novel RAB27A Variant Associated with Late-Onset Hemophagocytic Lymphohistiocytosis Alters Effector Protein Binding.

Autosomal recessive mutations in RAB27A are associated with Griscelli syndrome type 2 (GS2), characterized by hypopigmentation and development of early-onset, potentially fatal hemophagocytic lymphohistiocytosis (HLH). We describe a 35-year old male who presented with recurrent fever, was diagnosed with Epstein-Barr virus-driven chronic lymphoproliferation, fulfilled clinical HLH criteria, and who carried a novel homozygous RAB27A c.551G > A p.(R184Q) variant. We aimed to evaluate the contribution of the identified RAB27A variant in regard to the clinical phenotype as well as cellular and biochemical function. The patient displayed normal pigmentation as well as RAB27A expression in blood-derived cells. However, patient NK and CD8+ T cell exocytosis was low. Ectopic expression of the RAB27A p.R184Q variant rescued melanosome distribution in mouse Rab27a-deficient melanocytes, but failed to increase exocytosis upon reconstitution of human RAB27A-deficient CD8+ T cells. Mechanistically, the RAB27A p.R184Q variant displayed reduced binding to SLP2A but augmented binding to MUNC13-4, two key effector proteins in immune cells. MUNC13-4 binding was particularly strong to an inactive RAB27A p.T23N/p.R184Q double mutant. RAB27A p.R184Q was expressed and could facilitate melanosome trafficking, but did not support lymphocyte exocytosis. The HLH-associated RAB27A variant increased Munc13-4 binding, potentially representing a novel mode of impairing RAB27A function selectively in hematopoietic cells.

Cytokine and viral load kinetics in human herpesvirus 8-associated multicentric Castleman's disease complicated by hemophagocytic lymphohistiocytosis.

Human herpes virus 8 (HHV-8)-associated secondary hemophagocytic lymphohistiocytosis is a rare but critical immuno-hematological entity in immunocompetent patients. Establishing a diagnosis is challenging as is the monitoring of disease activity and therapeutic effects. We report a case of a HHV-8-associated hemophagocytic lymphohistiocytosis in a HIV-negative adult patient with multicentric Castleman's disease. As a novel finding, we report the use of certain inflammatory parameters, primarily interleukin-10 combined with viral load monitoring of the causative infectious agent in this case HHV-8 to monitor the clinical course of the hemophagocytic lymphohistiocytosis in the setting of bacterial septic complications.