Pediatric Pulmonary Multisystem Langerhans cell histiocytosis. Does lung lesion severity affect the outcome?

Abstract Background Pulmonary involvement in pediatric multisystem Langerhans cell histiocytosis (PPM LCH) is associated with either low risk (RO-) or high risk (RO+) organs. The nodulo-cystic lung lesions although pathognomonic, yet are very variable in severity and remain a source of controversy in certifying pulmonary LCH diagnosis. The study aimed to examine the prognostic value of clinical respiratory distress and radiological lung lesions severity. This is through associating a CT chest triad of bilateral, extensive and diffuse lesions. It is a retrospective study of 350 LCH patients who received systemic treatment at Children’s Cancer Hospital Egypt during the period from 2007 to 2020. Results Sixty-seven patients (67/350 − 19.1%) had PPM LCH at presentation. Severe lung lesions were present in 24 of them. The median follow-up period was 61 months (IQR: 3.4 to 8.3). The 5-year overall survival (OS) and event free survival (EFS) was 89% and 56.6% respectively. The EFS, for severe radiological lesions triad was 38% ± 20.7 versus 66% ± 16.2 for non-severe lesions p 0.002, while for concordant chest CT positive / X ray positive lesions 27% ± 22.344 versus discordant CT positive/X ray negative 66% ± 14.7 p 0.001, for clinical respiratory distress 13% ± 13.9 versus none 62% ± 22.9 p < 0.001, for RO- with severe lung lesions 47% ± 30.4 versus RO- without severe lung 69% ± 5.9 p0.04. There was a tendency for the independent prognostic impact of severe lung involvement; aHR = 1.7 (95% CI: 0.92 to 3.13, p = 0.09). Conclusion Although the lung is a low -risk organ per se in LCH, our study demonstrates a non negligeable prognostic impact of severe lung involvement in the risk stratification of pediatric LCH. This warrants further study and external validation.