Natural history of histiocytosis X: a Pediatric Oncology Group Study.

The best therapy for patients with histiocytosis X with disease involvement other than isolated bone lesions but without organ dysfunction is unclear. This retrospective study was undertaken to define the natural history of this group of patients. In 25 of the 92 studied patients, there was no progression of the disease after diagnosis. In 53 surviving patients, the disease either continuously progressed (40) or recurred intermittently (13). The onset of last disease activity was 24 months or less for 55% of these children. A fatal outcome occurred in 14 children. All of these children developed organ dysfunction and 11/14 died during or before the second year of disease. These three different outcomes could not be predicted from the parameters evaluated; however, the disease that never abated but was continuously active was associated with a suboptimal outcome, and the development of organ dysfunction was a grave prognostic sign.