Overview of Histiocytic Disorders
Histiocytic disorders are a group of diseases that occur when there is an over-production of white blood cells known as histiocytes that can lead to organ damage and tumor formation.
'Histio' = Tissue | 'Cyte' = Cell | 'Osis' - Too many
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This group of histiocytic disorders is made up of a wide variety of conditions that can affect both children and adults. In order to reduce confusion, in 1987, the Histiocyte Society classified these disorders into three groups based on the types of histiocyte cells involved:
Malignant Cell Disorders
This group includes certain kinds of leukemia and malignant tumors.
In 2016, the Histiocyte Society endorsed a revision, arranging the different histiocytoses into five main groups Langerhans related (L group), cutaneous and mucocutaneous histiocytoses (C group), Rosai–Dorfman disease (RDD) (R group), malignant histiocytoses (M group), and haemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (H group). This reclassification was based on research performed after 1987 that showed several new findings regarding the cell origins, molecular pathogenesis and clinical presentations.
The classification of these disorders has created a common name and language for the different histiocytic disorders. With the new system of classification, cooperative international clinical studies have been created for LCH and HLH. In these studies, patients are registered by their physicians to participate, and valuable information is gathered on all of the patients who are registered. The purpose is to evaluate information in order to improve current treatment options and outcomes, obtain information on new treatments, and provide direction for what research needs to be undertaken in the future. Those patients who are enrolled in clinical trials can benefit from the latest information about the treatment and care of the histiocytic disorders, as well as contribute to the international effort to improve outcome. Over the past 15-20 years, a vast amount of research, much of which has been funded by the Histiocytosis Association, has improved the understanding of LCH and HLH, as well as the more uncommon histiocytic disorders such as JXG, ECD and RDD. Guidelines for diagnosis, treatment, and follow-up of the histiocytic disorders have been created by the Histiocyte Society and the National Comprehensive Cancer Network.
Over the last ten years, Erdheim-Chester Disease (ECD), Langerhans cell histiocytosis (LCH), and Rosai Dorfman disease (RDD) have all been classified as rare cancers, or histiocytic neoplasms, by the World Health Organization (WHO). This is because of discoveries of cancer-causing mutations in nearly 50% cases of patients with RDD and >90% of ECD and LCH cases. It is also important to note how National Cancer Institute defines cancer: What Is Cancer? - NCI. Not all cancer spreads to other organs and some of the histiocytosis, especially. Rosai Dorfman disease can be very slow growing and even go away on their own (hence behave in a “benign” fashion). There are similar reports in other cancers as well.
Each of these diseases is very different, and the symptoms, rate of occurrence, diagnostic testing, and treatments vary widely. For more information about a particular histiocytic disorder, please see the corresponding pages.
Learn more about a specific histiocytic disease or related condition:
NCCN Histio Clinical Guidelines and Consensus Guidelines
NCCN Publishes Guidelines for LCH, ECD, and RDD
We are excited to share that the National Comprehensive Cancer Network® (NCCN®) - an alliance of leading cancer centers - announced the publication of new NCCN Guidelines® for histiocytosis. These clinical practice guidelines provide the latest evidence and expert-consensus for diagnosing and treating the three most common forms of histiocytosis in adults: Langerhans cell histiocytosis (LCH), Erdheim-Chester Disease (ECD,) and Rosai Dorfman Disease (RDD). Although the guidelines are focused on adult patients, there may be insight for pediatric physicians as well.
February 2023: There is a new way to learn more about NCCN and the various resources available to cancer patients.
You can download the free app here to view the Histiocytic Neoplasms guidelines. The Guidelines are currently focused for medical professionals however we hope to eventually help NCCN to develop patient guidelines as well.
The NCCN is comprised of 30 leading cancer centers that are dedicated to improving patient lives through research and education, and the development of valuable resources to help physicians, researchers, patients, and families. In a recent press release by NCCN, the Histiocytosis Association was honored to be able to share our excitement and support, alongside the ECD Global Alliance team and others.
"The Histiocytosis Association appreciates the dedication of all those involved at the NCCN for developing and publishing guidelines for three of the histiocytic disorders,” said Deanna Fournier, Executive Director, Histiocytosis Association. “As with all rare diseases, early diagnosis and awareness of the proper course of treatment has a very positive impact on patient outcomes; having access to the most up-to-date information at the ready will enable physicians around the world to continue to provide the best care to adults and children impacted by histiocytosis. We look forward to sharing the guidelines with our community."
The NCCN Guidelines can help patients, families and physicians access the latest information about symptoms, diagnosis, treatment, and more. They are useful tools when seeking approvals for coverage of drugs and therapies. They are available to access or download globally with a free NCCN account through their website or mobile app, which many physicians actively use in their practices. The guidelines are updated at least once a year and can be accessed at any time. You can view the published guidelines on NCCN’s website listed as “histiocytic neoplasms”. If using the guidelines outside of the United States, be sure to consult local healthcare providers about availability and coverage in other regions.
We encourage you to share these guidelines with your medical team.
If you have any questions, please do not hesitate to contact us. We are thrilled to be able to support the advancements of resources like these and look forward to sharing more with you in the coming weeks.
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(Guidelines are listed as "histiocytic neoplasms")
Histiocyte Society Publishes Consensus Guidelines for HLH
January 2023 - In January 2023, the Histiocyte Society published "HLH/MAS Consensus Management Efforts, Expert Help Diagnosing and Managing HLH", which curates the most recent consensus-based guidance manuscripts, organized by the HS and/or affiliated organizations and authored by HS experts, to assist with the diagnosis and management of HLH across many different contexts.
Access the Consensus Guidelines here.