Differential diagnosis of myxoid soft tissue tumors. Experience in the Clinical University Hospital of Valencia

Soft tissue tumors with myxoid components are often a diagnostic challenge for the pathologist. We retrospectively reviewed 41 cases of soft tissue tumors with myxoid components diagnosed in our center over a five-year period. The most frequent diagnoses were myxofibrosarcoma and myxoid liposarcoma, followed by low-grade fibromyxoid sarcoma, low-grade fibromyxoid tumor and myxoid neurofibroma. Other diagnoses included were extraskeletal myxoid chondrosarcoma, myxoinflammatory fibroblastic sarcoma, low-grade myxoliposarcoma, myofibrosarcoma, fibromatosis, solitary fibrous tumor, non-ossifying variant of ossifying fibromyxoid tumor and ancient neurinoma with myxoid degeneration. Immunohistochemical and molecular biology studies contributed significantly to the diagnosis. We highlight the importance of immunohistochemistry for MUC4 in the diagnosis of low-grade fibromyxoid sarcoma, and underscore the need for molecular studies in selected cases. Furthermore, several myxoid neoplasms present specific chromosomal translocations, therefore molecular biology studies to detect fusion genes are usually essential for the diagnosis. When the characteristics of the sample are not adequate for molecular biology, or no specific alterations are described, an in-depth knowledge of the histology of these lesions is still necessary to decide the most accurate diagnosis.