Rationale: Alveolar soft part sarcoma (ASPS) is a rare malignant soft tissue neoplasm with controversial histogenesis. ASPS accounts for 0.5% to 1% of all soft tissue sarcomas. Because of its rarity, ASPS is easily misdiagnosed, increasing the risk of incorrect treatment.
Patient concerns: A 6-year-old female patient presented with a history of a 2.0 × 2.5 × 3.0-cm mass in the deep soft tissues of her right lower extremity.
Diagnoses: Histopathological features indicated the diagnosis of ASPS. Microscopically, a diffuse arrangement of tumor cells or pseudoalveolar architectures separated by thin and well-vascularized fibrous septa were observed. Immunohistochemical staining of the tumor cells indicated positivity for transcription factor E3, myogenic determination factor 1, and periodic acid-Schiff-diastase (PAS-D) and showed a Ki-67 proliferating index of approximately 20%.
Interventions: The patient underwent enlarged resection of the tumor and was treated with radiotherapy.
Outcomes: During the 3-year follow-up, the patient has remained in good condition, with no symptom recurrence, distant metastatic spread, or significant toxicity during or after treatment. The patient remains under regular surveillance.
Lessons: Its low incidence, lack of characteristic clinical manifestations, and atypical location often lead to ASPS misdiagnosis and subsequent incorrect treatment. Nuclear expression of transcription factor E3 is of diagnostic value for ASPS. At present, there is no consensus on the treatment for ASPS. In-depth pathological analysis is needed to better understand the characteristics of this tumor.