Histiocytoses: emerging neoplasia behind inflammation.

Histiocytoses are disorders characterised by inflammation and the accumulation of cells derived from the monocyte and macrophage lineages, which results in tissue damage. Although they are often considered rare disorders with protean clinical manifestations, considerable advances in the understanding of their genetics have led to increased clinical recognition of these conditions, and fuelled further insights into their pathogenesis. In this Review, we describe insights into the cells of origin, molecular pathology, clinical features, and treatment strategies for some of the most common histiocytic disorders, including Langerhans cell histiocytosis, Erdheim-Chester disease, and Rosai-Dorfman disease. With the discovery of recurrent mutations affecting the mitogen-activated protein kinase and mTOR-AKT pathways in some of these histiocytoses, our understanding of these diseases has now evolved from the concept of a primary inflammatory condition to that of a clonal neoplastic disease. This understanding has led to the development of effective mechanism-based therapeutic strategies for patients with histiocytic diseases.

Revised classification of histiocytoses and neoplasms of the macrophage-dendritic cell lineages.

The histiocytoses are rare disorders characterized by the accumulation of macrophage, dendritic cell, or monocyte-derived cells in various tissues and organs of children and adults. More than 100 different subtypes have been described, with a wide range of clinical manifestations, presentations, and histologies. Since the first classification in 1987, a number of new findings regarding the cellular origins, molecular pathology, and clinical features of histiocytic disorders have been identified. We propose herein a revision of the classification of histiocytoses based on histology, phenotype, molecular alterations, and clinical and imaging characteristics. This revised classification system consists of 5 groups of diseases: (1) Langerhans-related, (2) cutaneous and mucocutaneous, and (3) malignant histiocytoses as well as (4) Rosai-Dorfman disease and (5) hemophagocytic lymphohistiocytosis and macrophage activation syndrome. Herein, we provide guidelines and recommendations for diagnoses of these disorders.

Management and Outcome of Patients With Langerhans Cell Histiocytosis and Single-Bone CNS-Risk Lesions: A Multi-Institutional Retrospective Study.

BACKGROUND: Children with Langerhans cell histiocytosis (LCH) and single-bone CNS-risk lesions have been reported to be at increased risk of diabetes insipidus (DI), central nervous system neurodegeneration (CNS-ND), and recurrence of disease. However, it is unknown whether the addition of chemotherapy or radiotherapy changes outcomes in these patients. METHODS: Ten pediatric institutions across North America and Europe contributed data of their patients with LCH and single-bone CNS-risk lesions. Clinical information on age, sex, specific craniofacial site involvement, and intracranial extension at diagnosis, therapy, and disease course was collected for all eligible patients. RESULTS: The final analysis included 93 eligible children who were either treated with systemic therapy (chemotherapy, chemo-radiotherapy, or radiotherapy) or local therapy (biopsy, curettage, and/or intralesional steroids). Fifty-nine patients had systemic and 34 had local therapy. The 5-year event-free survival (EFS) and overall survival (OS) were 80 ± 5% and 98 ± 2% in the systemic therapy group versus 85 ± 6% and 95 ± 5% in the local therapy group. There was no statistically significant difference between either group with regard to EFS (P = 0.26) and OS (P = 0.78). On multivariable analysis, there was no significant difference among the two treatment groups after adjusting for site and intracranial soft tissue extension, nor any trend favoring systemic therapy (HR = 2.26, 95% CI = 0.77-6.70; P = 0.14). CONCLUSION: Systemic therapy may not reduce the risk of recurrence or late sequelae in children with LCH and single-bone CNS-risk lesions as compared to local treatment.