Langerhans cell histiocytosis (LCH) is a rare disease characterized by clonal expansion of CD1a⁺CD207⁺ myeloid dendritic cells. The features of LCH are mainly described in children and remain poorly defined in adults; therefore, we conducted a nationwide survey to collect clinical data from 148 adult patients with LCH. The median age at diagnosis was 46.5 (range: 20–87) years with male predominance (60.8%). Among the 86 patients with detailed treatment information, 40 (46.5%) had single system LCH, whereas 46 (53.5%) had multisystem LCH. Moreover, 19 patients (22.1%) had an additional malignancy. BRAF V600E in plasma cell‐free DNA was associated with a low overall survival (OS) rate and the risk of the pituitary gland and central nervous system involvement. At a median follow‐up of 55 months from diagnosis, six patients (7.0%) had died, and the four patients with LCH‐related death did not respond to initial chemotherapy. The OS probability at 5 years post‐diagnosis was 90.6% (95% confidence interval: 79.8–95.8). Multivariate analysis showed that patients aged ≥60 years at diagnosis had a relatively poor prognosis. The probability of event‐free survival at 5 years was 52.1% (95% confidence interval: 36.6–65.5), with 57 patients requiring chemotherapy. In this study, we first revealed the high rate of relapse after chemotherapy and mortality of poor responders in adults as well as children. Therefore, prospective therapeutic studies of adults with LCH using targeted therapies are needed to improve outcomes in adults with LCH.

Reduction of leukemia cell burden and restoration of normal hematopoiesis at 3 months of crizotinib treatment in RAN-binding protein 2 (RANBP2)–anaplastic lymphoma kinase (ALK) acute myeloid leukemia

We applied two-step multicolor flow cytometry (FCM) for circulating lymphoma cells in the blood of 20 patients with angioimmunoblastic T-cell lymphoma (AITL) and confirmed neoplastic T-cells in all. Eleven exhibited dim expression of CD3 and 7 lost its expression. The proportion of CD10⁺ lymphoma cells ranged widely from 0 to 100%, with a median of 15.7%. Ten patients demonstrated expansion of a single T-cell receptor β-chain repertoire. Lymphoma cells comprised 0.01 to 18.22% (median, 0.26%) of white cells and the absolute numbers ranged from 0.5 to 1491.6 cells (median, 29.3 cells) per microliter of blood. We next found that 14 (70%) and 3 (15%) patients carried RHOA^G17V and IDH2^R172 mutations, respectively, in cell-free DNA (cfDNA) in the plasma. The combination of multicolor FCM of the blood, and tests for RHOA^G17V and IDH2^R172 hot-spot mutations in plasma cfDNA provides a blood-based ‘liquid biopsy’ for the diagnosis of AITL.