CHC-WEST 2016: News in Hematology: Mastocytosis

CHC-WEST 2016: News in Hematology: Mastocytosis
Dr. Minakshi Taparia - University of Alberta  

Mastocytosis has been defined in the literature as an abnormal accumulation of tissue mast cells in one or more organs. It is broadly separated in two categories - cutaneous (CM) and systemic (SM), which are seen in both children and adults. CM is a benign skin condition most commonly seen in children. It often resolves during puberty and is not associated with systemic involvement. Only small subsets are c-kit mutation positive. Alternatively, most adult are diagnosed with SM. Skin involvement is common and about 90-95 % patients have the c-kit mutation. They are classified based on WHO classification with major and minor criteria. Most patients are treated for symptoms by blocking the formation or action of mast cell mediators and cytoreductive treatment is reserved for other more aggressive variants. Several targeted therapeutic agents are in clinical trials and offer potentially more effective and specific treatments in the near future.

Histiocytes are bone marrow derived cells that protect the body from foreign substances by phagocytosing them and in some cases, using engulfed material to stimulate an immune response. Histiocytosis are diseases that are characterized by the uncontrolled accumulation of histiocytes with attendant tissue damage. They are now classified in 5 groups.

LCH is now considered a neoplastic disease based on the presence of somatic mutations in components of the RAS-RAF-MEK-ERK pathway in the majority of patients. It is classified based on number of organs involved as single system disease vs multisystem disease and sub classified as with risk organ and without risk organ involvement. The presence of mutations may now have implications for treatment and diagnosis.

A few words worth mentioning are on the relatively newly described entity of HLH. This was a clinical syndrome identified as a primary hereditary disease in infants and young children. In the recent years, there has been an explosion of information about the natural history of the disease and its molecular underpinnings. There is growing awareness of the unexpectedly common occurrence of this disorder in older age groups and the molecular basis for familial HLH and its relationship to the acquired forms seen in patients of all ages. It is also worth mentioning is the term MAS or Macrophage activation syndrome, which is features of HLH seen in association with systemic autoimmune disease and hence some differences in management.