# Pediatric Cutaneous Anaplastic Lymphoma Kinase-Positive Histiocytosis with DCTN1::ALK Fusion: A Case Report and Literature Search

## TL;DR

This paper reports a rare pediatric case of a skin tumor with a specific genetic fusion, DCTN1::ALK, and highlights the importance of molecular testing in diagnosis.

## Contribution

The first reported pediatric case of ALK-positive histiocytosis with the rare DCTN1::ALK fusion.

## Key findings

- The patient had a skin lesion with spindle cells and Touton-type giant cells.
- Molecular testing confirmed a DCTN1::ALK fusion and ALK rearrangement.
- The case emphasizes the need for molecular testing in ALK-positive histiocytosis.

## Abstract

Background and Clinical Significance: Anaplastic lymphoma kinase (ALK)-positive histiocytosis is a relatively novel entity, affecting single or multiple organ systems; it is characterized by aggregates of neoplastic cells of the histiocytic lineage, harboring molecular alterations in the ALK gene and exhibiting excellent response to systemic tyrosine kinase inhibitors. Case presentation: Herein, we present a pediatric case with cutaneous-only involvement: the 6-month-old male patient presented with an elevated, tan-colored lesion on his left forearm. Following surgical excision, histopathological evaluation reported spindle cells with wide eosinophilic cytoplasm and Touton-type giant cells. The tumor cells were positive for CD163, ALK, phosphorylated ERK, and cyclin D1. Fluorescent in situ hybridization revealed ALK rearrangement, whereas, upon next-generation sequencing, a DCTN1::ALK fusion was identified. Conclusion: Our case serves as a great addition to the limited number of cases reported in the literature, and it represents the first published pediatric case with the rare DCTN1::ALK fusion. The novelty of this genetic alteration and the lack of knowledge about its potential effects on the clinical aspects of ALK-positive histiocytosis highlight the importance of ancillary molecular testing, when available.