Aggressive unifocal bone Langerhans cell histiocytosis with soft tissue extension both responsive to radiotherapy: a case report

Abstract

Background: Langerhans cell histiocytosis (LCH) is a rare haematological neoplasm characterized by the accumulation of CD1a⁺, CD207/Langerin⁺ histiocytes within inflammatory lesions. LCH can involve any organ, but osteolytic bone lesions are most often encountered. Unifocal bone lesions may regress spontaneously after a thick needle biopsy has been taken.

Case presentation: In this case report, we describe the initial presentation of a single BRAF^V600E mutated osteolytic LCH lesion in the left proximal humerus of a 46-year-old previously healthy woman. Despite multiple surgical interventions, she unexpectedly experienced progressive disease manifestation with significant soft tissue extension to the surrounding musculature, subcutis and epidermis. Because the disease manifestation remained loco-regional, radiotherapy (RT) (total dose of 20 Gy in 10 fractions) was initiated.

Conclusion: The patient achieved a complete remission without any side effects. This case highlights that RT is a rational and relative mild local treatment option for patients with aggressive LCH affecting the bone and surrounding soft tissue.

Keywords: BRAF; Bone; LCH; Langerhans cell histiocytosis; Radiotherapy.

Fig. 1

Coronal X-ray (A) and gadolinium-enhanced T1-weighted MRI (B) images demonstrating a unifocal lesion in the left proximal humeral diaphysis at time of diagnosis. After seventeen months and two surgical interventions, axial gadolinium-enhanced T1-weighted MRI demonstrated progressive disease with significant soft tissue extension (C). Radiation treatment plan of the humerus. The planning target volume (PTV) is indicated by the red line, the clinical target volume (CTV) by the blue line, and gross tumor volume (GTV) by the yellow line (D). Three months following RT, T2-weighted MRI demonstrates a full radiological response (E). Successive PET-CT images show strong FDG uptake in the bone and surrounding soft-tissues, with a remarkable decrease in both tumoral mass and FDG uptake after RT, compatible with a complete radiological response (F). Abscess-like soft tissue extension through the skin prior to RT (G). Clinical response at 9 months post RT (20 Gy in 10 fractions) showing marked improvement of skin and subcutis inflammation (H)

Fig. 2

Hematoxylin and eosin (HE) and immunohistochemical stains of a thick needle biopsy demonstrate a dense infiltrate of CD1a and CD207 positive histiocytes with variable S100 expression (A). Immunohistochemical analysis of lesional tissue obtained at surgical debridement shows CD207 positive histiocytes and multinucleated giant cells (B). Histopathological analysis of a biopsy taken at time of disease progression demonstrates CD1a and CD207 positive histiocytes, indicative of active LCH, with frequent nuclear indentations and rare mitoses—one of which is shown (C)