Uncommon but intriguing: A pediatric primary histiocytic sarcoma case-Clinical insights and literature review

Abstract

Histiocytic sarcoma (HS) is a rare and aggressive malignancy derived from histiocytes, accounting for less than 1% of hematopoietic neoplasms. Pediatric soft tissue involvement is exceptionally rare, with limited data to guide management. We present the case of a 5-year-old girl with a painless mass on the right thigh. Imaging revealed a malignant intra-aponeurotic soft tissue lesion. Histopathological analysis confirmed HS with immunohistochemical positivity for CD68, CD31, LCA, and INI1, and a Ki-67 index of 40%. Staging PET-CT identified local lymph node involvement. Following R1 surgical resection, the patient received adjuvant radiotherapy (43 Gy to the tumor bed and 36.9 Gy to the inguinal region) and OEPAbased chemotherapy. At 20 months post-treatment, the patient remains in remission with excellent functional outcomes. This case highlights the rarity of soft tissue histiocytic sarcoma in pediatric patients and the importance of multimodal treatment to achieve long-term remission.

Keywords: Histiocytic; Oncology; Pediatric cancer; Radiotherapy; Soft tissue sarcoma.

Fig. 1

T1-weighted MRI with gadolinium injection showing a 35 × 25 × 59 mm intra-aponeurotic, extra-muscular tumor mass located in the anterolateral region of the right thigh. The lesion appears hyperintense on T1, with heterogeneous enhancement postcontrast. These findings suggest an infiltrative soft tissue mass, with features suspicious for malignancy.

Fig. 2

Staging with 18F-FDG PET-CT demonstrating a hypermetabolic tumor in the anterolateral aspect of the right thigh, with a SUVmax of 19.4, indicative of intense glucose uptake. A mildly hypermetabolic right inguinal lymph node (SUVmax = 1) was also noted.

Fig. 3

Dosimetric data and dose distrubition. (A) Axial slice from the dosimetric CT scan showing the distribution of the 95% isodose at the left inguinal region, corresponding to the site of the initially identified inguinal lymphadenopathy. (B) Sagittal slice demonstrating the distribution of the 95% isodose at the operative bed of the primary tumor, where a bolus is applied to ensure adequate dose delivery to the superficial tissues. (C and D) 3D reconstruction illustrating the distribution of different isodoses and their relationship with surrounding anatomical structures, including the growth plates (physis), with treatment delivered using VMAT (Volumetric Modulated Arc Therapy) to optimize dose conformity while sparing healthy tissues, especially the growth plates.

Fig. 4

(A) Pretreatment 18F-FDG PET-CT showing a hypermetabolic tumor at the primary site with an SUVmax of 19.4. (B) Post-treatment 18F-FDG PET-CT (3 months after the end of treatment) showing complete resolution of the metabolic activity at the primary tumor site, with no detectable abnormal uptake, indicating total remission and a favorable response to treatment.