Abstract
Fibrosarcoma represent a rare group of soft tissue malignancies derived from fibrous connective tissue and immature proliferating fibroblasts or undifferentiated anaplastic spindle cells. It affects patients in the fourth and fifth decade of life. Fibrosarcomas can be classified in subtypes such as low-grade fibromyxoid sarcoma (LGFMS) and sclerosing epithelioid fibrosarcoma (SEF), and others. Histological features that overlap between types of fibrosarcomas is well known and reported in the literature. We report the case of a 53-year-old patient who presented a tumor in the axillary fossa, which was initially diagnosed as a solitary fibrous tumor. Due to recurrence of the lesion, as well as the presence of distant metastases, the histological revision considered the diagnosis of breast metaplastic carcinoma, since the tumor expressed the p63 antigen and estrogen and progesterone receptors. Unexpected resistance to chemotherapy motivated the diagnosis re-evaluation, which was due to MUC4 expression and morphological characteristics concluded by a hybrid LGFMS-SEF tumor. The authors call attention to the difficult diagnosis in cases of soft tissue tumors. A broad panel of immunohistochemical research is required as the clinical course is essential to the final diagnosis.