Notable therapeutic response in a patient with systemic juvenile xanthogranuloma with KIF5B-ALK fusion

ALK-positive histiocytosis involving the cavernous sinus: A deceptive radiologic mimic of meningioma

Anaplastic lymphoma kinase (ALK)-positive histiocytosis is an uncommon condition, recently considered a separate condition from other histiocytosis by WHO 5th edition. It can involve intracranial structures. This manuscript describes a case of ALK-positive histiocytosis of the cavernous sinus, focusing on the radiologic and pathologic presentation of the entity. Our case had MRI manifestations mimicking meningioma, metastasis, and Langerhans histiocytosis. On CT imaging, benign osseous remodeling of the cavernous sinus was detected, which can be helpful in differentiating it from more common meningioma.

Systemic juvenile xanthogranuloma: A systematic review

OBJECTIVE

To perform a systematic review to investigate the available literature regarding systemic juvenile xanthogranuloma (SJXG) and report the population characteristics, clinical manifestation, therapy, and outcome.

REVIEW METHODS

A search of PubMed, Embase, and Cochrane Library for all articles published between 1981 and 2022 was performed with variations and combinations of the following search terms: extracutaneous, visceral, systemic, and juvenile xanthogranuloma (JXG). Data extracted included demographics, organ involvement, treatment, outcome, and permanent sequelae.

RESULTS

A total of 103 articles encompassing 159 patients met the inclusion criteria. The median onset age was 9 months, with a male predominance (61%). The distribution of major involved organs varied by age, and younger onset age was associated with more organ involvement. The most commonly involved site was the central nervous system (CNS) (40.9%), followed by the liver (31.4%), the lung (18.9%), and the eye (18.2%). At the termination of follow-up, 93 patients (58.5%) were alive with no disease, 56 (35.2%) were alive with disease, and 10 (6.3%) were dead of disease. There was a significant difference in outcome between patients with and without spleen involvement (p = .0003), and patients with spleen involvement suffered a higher risk of death. Permanent sequelae mainly comprised CNS symptoms and ocular manifestations.

CONCLUSIONS

SJXG can involve varying numbers and combinations of extracutaneous sites. There is no standard therapy for SJXG and clinicians should choose individualized therapy modalities.

ALK-positive histiocytosis: a new clinicopathologic spectrum highlighting neurologic involvement and responses to ALK inhibition

ALK-positive histiocytosis is a rare subtype of histiocytic neoplasm first described in 2008 in 3 infants with multisystemic disease involving the liver and hematopoietic system. This entity has subsequently been documented in case reports and series to occupy a wider clinicopathologic spectrum with recurrent KIF5B-ALK fusions. The full clinicopathologic and molecular spectra of ALK-positive histiocytosis remain, however, poorly characterized. Here, we describe the largest study of ALK-positive histiocytosis to date, with detailed clinicopathologic data of 39 cases, including 37 cases with confirmed ALK rearrangements. The clinical spectrum comprised distinct clinical phenotypic groups: infants with multisystemic disease with liver and hematopoietic involvement, as originally described (Group 1A: 6/39), other patients with multisystemic disease (Group 1B: 10/39), and patients with single-system disease (Group 2: 23/39). Nineteen patients of the entire cohort (49%) had neurologic involvement (7 and 12 from Groups 1B and 2, respectively). Histology included classic xanthogranuloma features in almost one-third of cases, whereas the majority displayed a more densely cellular, monomorphic appearance without lipidized histiocytes but sometimes more spindled or epithelioid morphology. Neoplastic histiocytes were positive for macrophage markers and often conferred strong expression of phosphorylated extracellular signal-regulated kinase, confirming MAPK pathway activation. KIF5B-ALK fusions were detected in 27 patients, whereas CLTC-ALK, TPM3-ALK, TFG-ALK, EML4-ALK, and DCTN1-ALK fusions were identified in single cases. Robust and durable responses were observed in 11/11 patients treated with ALK inhibition, 10 with neurologic involvement. This study presents the existing clinicopathologic and molecular landscape of ALK-positive histiocytosis and provides guidance for the clinical management of this emerging histiocytic entity.