Pheochromocytomas and extra-adrenal paragangliomas are rare tumors arising from neural crest tissue that develops into sympathetic and parasympathetic paraganglia throughout the body.
The most recent World Health Organization classification utilizes the term pheochromocytoma exclusively for tumors arising from the adrenal medulla, and the term extra-adrenal paraganglioma for similar tumors that arise from other locations.
Incidence and Mortality
The incidence of pheochromocytoma is 2...
Reactivation of Langerhans cell histiocytosis (LCH) after complete response has been reported; usually occurring within the first 9 to 12 months after stopping treatment. The percentage of patients with reactivations was 9% to 17.4% for single-site disease; 37% for single-system, multifocal disease; 46% for multisystem (nonrisk organ) disease; and 54% for patients with risk-organ involvement. Forty-three percent of reactivations were in bone, 11% in ears, 9% in skin, and 7% developed diabetes insipidus; a lower percentage of patients had lymph node, bone marrow, or risk-organ relapses. The median time to reactivation was 12 to 15 months in nonrisk patients and 9 months in risk patients. One-third of patients had more than one reactivation varying from 9 to 14 months after the initial reactivation. Patients with reactivations were more likely to have long-term sequelae in the bones, diabetes insipidus, or other endocrine, ear, or lung problems.
A comprehensive review of the German-Austrian-Dutch (Deutsche Arbeits-gemeinschaft für Leukaemieforschung und-therapie im Kindesalter [DAL]) and Histiocyte Society clinical trials revealed a reactivation rate of 46% at 5 years for patients with multisystem LCH, with most reactivations occurring within 2 years of first remission. A second reactivation occurred in 44%, again within 2 years of the second remission. Involvement of the risk organs in these reactivations occurred only in those who were initially in the high-risk group (meaning they had liver, spleen, or bone marrow involvement at the time of original diagnosis).[Level of evidence: 3iiiDiii] Most reactivations, even in patients with high-risk disease who initially responded to therapy, were in bone, skin, or other nonrisk locations.
The percentage of reactivations in multisystem disease was identical in the Japanese trial, [Level of evidence: 1iiA] and the LCH-II trial  (45% and 46%, respectively). There was not a statistically significant difference in reactivations between the high-risk and low-risk groups. Both the DAL-HX and Japanese studies concluded that intensified treatment increased rapid response, particularly in young children and infants younger than 2 years, and together with rapid switch to salvage therapy for nonresponders, reduced mortality for patients with high-risk multisystem LCH.