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BackgroundWe evaluated the effectiveness of FDG‐PET scans in identifying sites of active disease and assessing response to therapy in patients with Langerhans cell histiocytosis (LCH). Changes in standardized uptake value (SUV) indicated increased or decreased disease activity before changes are evident by plain films or bone scans.MethodsOne hundred and two PET scans for 44 patients (41 children, 3 adults) with biopsy‐proven LCH were compared with 83 corollary imaging modalities and were rated for overall clinical utility: false positive or negative (“inferior”), confirming lesions identified by another imaging modality (“confirmatory”), or showing additional lesions, response to therapy or recurrence of disease activity (“superior”), in comparison to bone scans, MRI, CT or plain films.ResultsFDG‐PET was rated superior in that 90/256 (35%) new, recurrent, or lesions responding to therapy were identified via change in standard uptake value (SUV) before other radiographic changes. PET scans confirmed active LCH in 146/256 (57%). FDG‐PET was superior to bone scans in that 8/23 (34%) lesions, 11/53 (21%) comparisons to lesions found by MRI, 13/64 (20%) CT, and 58/116 (50%) plain films. PET scans confirmed lesions found by: 14/23 (61%) bone scans, 33/53 (62%) MRI, 45/64 (65%) CT, and 54/116 (46%) of plain films.ConclusionsWhole body FDG‐PET scans can detect LCH activity and early response to therapy with greater accuracy than other imaging modalities in patients with LCH lesions in the bones and soft tissues. Whole‐body FDG‐PET scanning is an important and informative study at diagnosis and for following disease course in patients with LCH. Pediatr Blood Cancer 2009;52:97–101. © 2008 Wiley‐Liss, Inc.

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