Background Lung involvement in childhood Langerhans cell histiocytosis (LCH) is infrequent and rarely life threatening, but occasionally, severe presentations are observed. Methods Among 1482 children (< 15 years) registered in the French LCH registry (1994–2018), 111 (7.4%) had lung involvement. This retrospective study included data for 17 (1.1%) patients that required one or more intensive care unit (ICU) admissions for respiratory failure. Results The median age was 1.3 years at the first ICU hospitalization. Of the 17 patients, 14 presented with lung involvement at the LCH diagnosis, and 7 patients (41%) had concomitant involvement of risk-organ (hematologic, spleen, or liver). Thirty-five ICU hospitalizations were analysed. Among these, 22 (63%) were secondary to a pneumothorax, 5 (14%) were associated with important cystic lesions without pneumothorax, and 8 (23%) included a diffuse micronodular lung infiltration in the context of multisystem disease. First-line vinblastine–corticosteroid combination therapy was administered to 16 patients; 12 patients required a second-line therapy (cladribine: n = 7; etoposide-aracytine: n = 3; targeted therapy n = 2). A total of 6 children (35%) died (repeated pneumothorax: n = 3; diffuse micronodular lung infiltration in the context of multisystem disease: n = 2; following lung transplantation: n = 1). For survivors, the median follow-up after ICU was 11.2 years. Among these, 9 patients remain asymptomatic despite abnormal chest imaging. Conclusions Severe lung involvement is unusual in childhood LCH, but it is associated with high mortality. Treatment guidelines should be improved for this group of patients: viral infection prophylaxis and early administration of a new LCH therapy, such as targeted therapy.

Summary BRAF inhibitors are an effective treatment for BRAFV600E‐mutated, risk‐organ‐positive Langerhans cell histiocytosis (RO+ LCH). However, cell‐free BRAFV600E DNA often persists during therapy and recurrence frequently occurs after therapy discontinuation. To identify a pathological reservoir of BRAFV600E‐mutated cells, we studied peripheral blood cells obtained from six infants with RO+ multisystem (MS) LCH that received targeted therapy. After cell sorting, the BRAFV600E mutation was detected in monocytes (n = 5), B lymphocytes (n = 3), T lymphocytes (n = 2), and myeloid and plasmacytoid dendritic cells (n = 2 each). This biomarker may offer an interesting tool for monitoring the effectiveness of new therapeutic approaches for weaning children with RO+ LCH from targeted therapy.

Ten to fifteen percent of children with acute lymphoblastic leukemia (ALL) relapse following treatment. Of these, less than 2% display ophthalmic relapses, which owing to their scarcity, are largely undocumented, leaving clinicians with few diagnostic and therapeutic recommendations, despite serious functional sequelae. We conducted a French multicenter retrospective study to collect all clinical, radiological, biological, and therapeutic data, and outcomes for children with ALL ophthalmic relapses. From 2000 to 2020, 20 ophthalmic relapses occurring after first-line therapy performed before January 1 st , 2017 were included in our study: 14 B-ALL and 6 T-ALL. Fifteen patients (75%) had concomitant involvement of the central nervous system, and 11 (55%) a combined bone marrow relapse. Only 1 had an isolated ophthalmic relapse. Eight children (40%) died, 7 from a refractory disease and 1 from toxic death, and 4 patients relapsed. With a median follow-up of 63.1 months, 8 patients are currently alive in continuous complete remission with only 2 displaying severe ophthalmic sequelae. Although rare, ophthalmic relapse could have a significant impact on the functional prognosis of survivors. Their management must be multidisciplinary, with a central role given to ophthalmologists.