Chondroblastoma of the proximal femur: Case report with a diagnostic challenge and brief literature review

Chondroblastoma is a rare benign cartilaginous neoplasm accounting for fewer than 1% of all primary bone tumors, with a well-established predilection for the epiphyses of long bones in skeletally immature patients. Its occurrence in a skeletally mature adult, combined with a large lesion size and metaphyseal extension, poses a distinct diagnostic and surgical challenge. 
We report the case of a 28-year-old male who presented with several months of progressive right hip and groin pain. Imaging demonstrated a well-defined eccentric lytic lesion of the proximal femoral epiphysis measuring approximately 5.5 cm, with extension into the femoral neck and metaphysis. Following multidisciplinary tumor board review, CT-guided core needle biopsy was performed. Histopathological examination and immunohistochemistry (IHC) studies confirmed chondroblastoma. Molecular analysis identified the defining H3F3B K36M hotspot mutation, confirming the diagnosis and excluding principal mimickers. 
The patient underwent extended intralesional curettage with high-speed burring, chemical adjuvant therapy, and reconstruction with bone graft and calcium sulfate pellets. Local recurrence was detected at 18 months, requiring a second curettage. The patient ultimately achieved full functional recovery without further evidence of disease. 
This case illustrates the diagnostic complexity of chondroblastoma in an adult, underscores the indispensable role of molecular confirmation, and highlights the known risk of local recurrence at the proximal femur, a site recognized as particularly challenging for surgical access and local control.