Clear Cell Sarcoma of the Pelvis in a Male Child, Diagnosed Using Ancillary Techniques - A Rare Case Report

Clear cell sarcoma is a rare malignant neoplasm of uncertain differentiation that typically arises in the deep soft tissues, most frequently involving the tendons and aponeuroses of the extremities in young adults, particularly females. Diagnostic challenges often arise due to its striking histological and immunohistochemical resemblance to metastatic malignant melanoma. We report an exceptionally rare case of clear cell sarcoma occurring in a nine-year-old male child, located in the pelvis with direct extension into the right pelvic bone. Non-Contrast Computed Tomography (NCCT) and Magnetic Resonance Imaging (MRI) demonstrated tumour extension into the presacral space with intraspinal involvement, resulting in widening of the spinal canal and neural foramina. Trucut biopsy revealed nests of epithelioid to spindle-shaped cells with clear to eosinophilic cytoplasm and prominent nucleoli. Bone marrow aspiration from the right iliac region yielded tumour cells, confirming marrow infiltration. The diagnosis was established through a multimodal approach integrating radiological assessment, bone marrow aspiration cytology, and trucut core biopsy findings. Ancillary studies, including flow cytometry, immunohistochemistry, and special stains, further supported the diagnosis in this challenging presentation. A review of the relevant literature is provided, highlighting distinguishing features from morphologically similar lesions to enhance recognition of this aggressive, metastasis-prone malignancy.