Langerhans cell histiocytosis is a neoplasm and consequently its recurrence is a relapse: In memory of Bob Arceci

Langerhans cell histiocytosis (LCH) remains a poorly understood disorder with heterogeneous clinical presentations characterized by focal or disseminated lesions that contain excessive CD1a+ langerin+ cells with dendritic cell features known as “LCH cells.” Two of the major questions investigated over the past century have been (i) the origin of LCH cells and (ii) whether LCH is primarily an immune dysregulatory disorder or a neoplasm. Current opinion is that LCH cells are likely to arise from hematopoietic precursor cells, although the stage of derailment and site of transformation remain unclear and may vary in patients with different extent of disease. Over the years, evidence has provided the view that LCH is a neoplasm. The demonstration of clonality of LCH cells, insufficient evidence alone for neoplasia, is now bolstered by finding driver somatic mutations in BRAF in up to 55% of patients with LCH, and activation of the RAS‐RAF‐MEK‐ERK (where MEK and ERK are mitogen‐activated protein kinase and extracellular signal‐regulated kinase, respectively) pathway in nearly 100% of patients with LCH. Herein, we review the evidence that recurrent genetic abnormalities characterized by activating oncogenic mutations should satisfy prerequisites for LCH to be called a neoplasm. As a consequence, recurrent episodes of LCH should be considered relapsed disease rather than disease reactivation. Mapping the complete genetic landscape of this intriguing disease will provide additional support for the conclusion that LCH is a neoplasm and is likely to provide more potential opportunities for molecularly targeted therapies.     

Spontaneous Gonadotrophin Deficiency Recovery in an Adult Patient with Langerhans Cell Histiocytosis (LCH)

Langerhans cell histocytosis (LCH) is a rare disease which exhibits a particular predilection for pituitary involvement leading to diabetes insipidus (DI) and other anterior pituitary hormonal deficiencies that are usually permanent and unresponsive to treatment. We report a 35 year old woman with a 10 year history of multisystemic LCH who developed DI, mild hyperprolactinemia, gonadotrophin and partial growth hormone deficiency following a normal delivery that was accompanied with infundibular thickening on pituitary magnetic resonance imaging (MRI). Following several courses of glucocorticoid administration, that were not associated with any substantial improvement, the patient was started on estrogen replacement therapy and cabergoline. After a three year period free of further relapses she developed irregular uterine bleeding. Following estrogen and cabergoline discontinuation she resumed normal menstruation while a repeated MRI of the pituitary showed an almost normal infundibulum. Endocrine investigation revealed normal gonadotrophin axis and prolactin levels, while the patient continues to menstruate, every 30–40 days, ten months after the resumption of her menstrual cycle. This case demonstrates for the first time that LCH induced pituitary deficiencies can run a variable clinical course and even spontaneously recover.     

Endocrine involvement in pediatric-onset Langerhans' cell histiocytosis: a population-based study

OBJECTIVE: To document the frequency and outcome of endocrine involvement in pediatric-onset Langerhans' cell histiocytosis (LCH), and the association with other types of organ involvement. STUDY DESIGN: This retrospective nationwide multicenter study involved 589 patients with pediatric-onset LCH, 148 of whom had endocrine dysfunction. Median follow-up was 11.6 years. RESULTS: Pituitary dysfunction was present in 145 patients, and 141 had diabetes insipidus (DI). The estimated 10-year risks of pituitary involvement were 24.2% +/- 1.8%. GH deficiency occurred in 61 patients. Median age at onset was 2.8 years for LCH, 3.9 years for DI, and 7.7 years for GH deficiency. The risk of cranial involvement; ear, nose, and throat involvement; pneumothorax; and cholangitis was significantly higher in patients with endocrinopathy. The chronology of episodes did not support a causal link between pituitary involvement and involvement of other organs. Systemic treatment of LCH did not prevent pituitary involvement. The most severe complication was a neurodegenerative syndrome, which affected 4.3% and 10.8% of patients, respectively, 5 and 15 years after initial diagnosis, and appeared to be linked to pituitary involvement. CONCLUSION: Patients who develop endocrine LCH disorders are at a high risk of neurodegenerative LCH and require long-term follow-up.     

The use of BRAF V600E mutation‐specific immunohistochemistry in pediatric Langerhans cell histiocytosis

BRAF p.V600E mutations are detected in greater than 50% of pediatric Langerhans cell histiocytosis (LCH) lesions. However, the use of mutation‐specific BRAF V600E immunohistochemistry (IHC) as a surrogate for molecular testing in pediatric LCH is unknown. We tested the mutation‐specific BRAF V600E monoclonal antibody (clone VE1) in formalin‐fixed, paraffin‐embedded LCH samples from 26 pediatric patients (14 males and 12 females, ages 7 mo–17 y) using allele‐specific real‐time polymerase chain reaction (PCR) with a limit of detection of 0.5% as the comparative gold standard. BRAF VE1 staining was scored for both intensity (0‐3+) and percentage of immunoreactive tumor cells (0%‐100%). BRAF VE1 immunoreactivity was determined using both lenient (≥1+, ≥1%) and stringent (≥2+, ≥10%) scoring criteria. Using lenient‐scoring criteria, we found that the sensitivity and specificity of IHC compared with allele‐specific real‐time PCR were 100.0% and 18.2%, respectively. The poor specificity of lenient IHC analysis was attributable to weak, 1+ staining in both BRAF‐mutated and wild‐type LCH. Using stringent‐scoring criteria, we found that specificity improved to 100.0% at the expense of sensitivity that decreased to 80.0%. Stringent scoring generated 3 false‐negative results, but in all cases, neoplastic tissue comprised less than 5% of the stained section and/or the specimen was decalcified. In conclusion, highly sensitive molecular assays remain the gold standard for BRAF mutation analysis in LCH paraffin‐embedded lesions. To avoid false‐positive results, unequivocal VE1 staining of 2+ intensity in greater than or equal to 10% neoplastic histiocytes is required. However, negative VE1 results require additional studies to exclude false‐negatives, and stringent‐scoring criteria may not be optimal for scant or decalcified specimens.     

Langerhans cell histiocytosis: Current concepts and treatments

Langerhans cell histiocytosis (LCH) is a rare proliferative disorder of cells with the phenotype of activated Langerhans cells. The diagnosis of LCH is often delayed or missed. Many questions about LCH remain to be answered, including whether it is caused by a malignancy or by immune dysregulation. Data from the early 1990s showed that LCH consisted of an accumulation of monoclonal LCH cells, suggesting a neoplastic disorder. However, further investigations with current sophisticated techniques have not shown consistent genomic aberrations. Recent data which suggests a role for an IL-17A dependant pathway of dendritic cell fusion in LCH remains to be proven. The most recent data taken together swing the pendulum towards an immunologic aberration.     

Development of Langerhans cell histiocytosis associated with chronic active Epstein-Barr virus infection

Chronic active Epstein-Barr virus (CAEBV) infection is characterized by a status of lymphoproliferative disease of EBV-infected cells, resulting in chronic or recurrent infectious mononucleosis-like symptoms. CAEBV is always accompanied by life-threatening complications. We report the case of a 2-year-old female patient with CAEBV who subsequently developed Langerhans cell histiocytosis (LCH) presenting with bilateral exophthalmos, bone, and skin involvement. In situ hybridization for EBER revealed EBV-infected B-cells present in lesional tissue implying that interactions between EBV-infected B-cells and lesional Langerhans cells may be associated with the development of LCH.     

Pulmonary Langerhans cell histiocytosis in children: A spectrum of radiologic findings

Pulmonary Langerhans cell histiocytosis (PLCH) is a well known entity in adults but is exceedingly rare in children. It is better described in adults than in children. We describe the current understanding of PLCH in children and a spectrum of radiological findings of PLCH in the paediatric population. On high resolution computed tomography (HRCT), PLCH may have variable appearance depending on the stage of disease, ranging from small interstitial nodular opacities to multiple thin/thick walled cysts (often bizarre in shape), eventually leading to marked parenchymal fibrosis and honeycomb pattern. CT finding of PLCH is similar in adult and paediatric populations with the exception that lung base near the costophrenic angle is spared in adults but almost always involved in children.