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

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.