Histology of LCH lesions. This figure depicts a typical LCH lesion with characteristic histology. Pathologic “histiocytes” with reniform nuclei and eosinophilic cytoplasm are scattered among an infiltrate of lymphocytes, eosinophils, and macrophages. The LCH cells react to immunostains for CD207, CD1a, and S100, but not for fascin or factor XIIIa. This biopsy could be from any child or adult with low- or high-risk LCH. H&E, hematoxylin and eosin. Images courtesy of John Hicks, Baylor College of Medicine.