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What Is Histiocytosis

Histiocytosis is a rare blood disease that is caused by an excess of white blood cells called histiocytes. The histiocytes cluster together and can attack the skin, bones, lungs, liver, spleen, gums, ears, eyes and/or the central nervous system. The disease can range from limited involvement that spontaneously regresses to progressive multi-organ involvement that can be chronic and debilitating. In some cases the disease can be life threatening.

In some ways, histiocytosis is similar to cancer and has historically been treated by oncologists with chemotherapy and/or radiation. Unlike cancer, histiocytosis sometimes goes into remission without treatment. The vast majority of people diagnosed with histiocytosis are children under the age of ten, but it is also found in adults of all ages.

Histiocytosis affects roughly 1 in 200,000 children born each year in the United States. Histiocytosis is so rare that there is little research into its cause and treatment and is often referred to as an "orphan disease", meaning it strikes too few people to generate government-supported research.


Hemophagocytic Lymphohistiocytosis (HLH) is a rare form of histiocytosis. It is a disorder of the immune system primarily affecting young infants and children. The prevalence of HLH is 1.2 in every 1,000,000 children under the age of 15. We currently know that HLH occurs either on the basis of genetic defect or as a secondary form with underlying diseases such as infections, cancer, or rheumatic disease. The onset of HLH is usually early in life and a persistent cure can only be achieved with aggressive chemotherapy treatments and successful Bone Marrow Transplant.