# An Adult Case of Chest Wall Langerhans Cell Histiocytosis Mimicking Malignancy and Responding to Targeted Therapy

## TL;DR

A rare case of chest wall Langerhans cell histiocytosis in an adult was misdiagnosed as malignancy but successfully treated with targeted therapy after molecular testing.

## Contribution

This case highlights the diagnostic challenge of adult LCH mimicking malignancy and demonstrates the effectiveness of BRAF/MEK inhibition in treatment.

## Key findings

- Adult chest wall LCH can radiographically resemble malignancy, requiring biopsy for diagnosis.
- Molecular testing identified a BRAF V600E mutation, leading to successful treatment with dabrafenib and trametinib.
- Targeted BRAF/MEK inhibition may be an effective therapeutic option when conventional treatments fail.

## Abstract

Langerhans cell histiocytosis (LCH) is a rare clonal proliferation of dendritic cells that is exceptionally uncommon in adults and only rarely affects the chest wall. Adult rib lesions often radiographically mimic malignancy, necessitating biopsy for accurate diagnosis.

We report the case of a 52-year-old woman with Class III (severe) obesity and newly diagnosed type 2 diabetes who developed a painful right chest wall mass following severe coughing during coronavirus disease 2019 (COVID-19). Imaging revealed a lobulated lesion with rib erosion and pleural indentation concerning for malignancy. Surgical debridement yielded histiocytic inflammation, and cultures grew Staphylococcus epidermidis. Final histopathology confirmed LCH. Despite wound re-closures and antibiotic therapy, persistent drainage continued until molecular testing identified a B-Raf proto-oncogene, serine/threonine-protein kinase (BRAF) V600E mutation. Targeted therapy with dabrafenib and trametinib was initiated, resulting in rapid clinical improvement and complete wound healing.

Adult chest wall LCH represents a rare diagnostic challenge due to its malignant radiographic appearance. Histopathologic confirmation, with molecular testing, is essential, and targeted BRAF/mitogen-activated protein kinase kinase (MEK) inhibition may provide an effective therapeutic option when conventional measures fail.