Aggressive Langerhans cell histiocytosis following T‐cell acute lymphoblastic leukemia

A 4‐year‐old female child developed cutaneous Langerhans cell histiocytosis 6 months following a diagnosis of T‐cell acute lymphoblastic leukemia. Imaging revealed no evidence of systemic disease. Seven months later, the first systemic lesion was discovered on laryngoscopy. Restaging Positron Emission Tomography ‐ Computed Tomography at that time revealed new 18‐fluorodeoxyglucose‐positive lesions in the left apical pleural margin, right lower peri‐esophageal region, left ventricular myocardium, pancreas, upper pole of the left kidney, and inguinal and gluteal regions consistent with progressive systemic disease. Genomic testing revealed a low tumor mutational burden as well as mutations in KRAS G12A, ARID1A Q524, CDKN2A/B loss, and an alteration in NOTCH1.