A Case Report of a Rare Entity - Lateral End of Clavicle Chondromyxoid Fibroma which was Mistaken as Giant Cell Tumor and Aneurysmal Cyst.

Introduction: The clavicle is an uncommon site for tumors, as it is a flat bone and rarely affected by neoplasms. Most clavicular tumors are malignant, with metastases and Ewing's sarcoma being the most common. Overall, clavicular neoplasms account for <1% of all bone tumors, and chondromyxoid fibroma (CMF) is particularly rare, comprising <1% of cases. This tumor typically arises in the metaphysis of the proximal tibia.

Case report: A young male patient comes with lateral end clavicle swelling, which on radiologically was diagnosed giant cell tumor. Later on, needle biopsy was thought to be an aneurysmal bone cyst (ABC). Finally, it turned out to be CMF on biopsy.

Conclusion: This case report presents a rare instance in which CMF was initially misdiagnosed as a giant cell tumor based on radiological findings and later as an ABC after histopathological examination. The definitive diagnosis of CMF was only confirmed following excisional biopsy.