A pelvic cavity malignant solitary fibrous tumor with dedifferentiation and multifocal cytokeratin expression

Abstract Background: Solitary fibrous tumor is an uncommon mesenchymal neoplasm that originates from fibroblasts and occurs predominantly in the visceral pleura. Pelvic cavity small sized malignant solitary fibrous tumor is very rare; it is easily misjudged by surgeons as a benign lesion and resected by laparoscopic surgery. When accompanied by dedifferentiation, malignant solitary fibrous tumor is difficult to diagnose by pathologists. Here, we describe a challenging case.Case presentation: A 47-year-old man was accidentally found to have a pelvic mass for three months, with pain and distension for seven days. The mass was adhered and compressed to the ureter and bladder. The right side of the pelvic cavity had a palpable and substantial mass, with no obvious associated pain. With an assumed diagnosis of a benign tumor, the patient underwent laparoscopic surgery to resect the tumor. Histologically, spindle cell areas and dedifferentiated areas were observed. Immunohistochemical analysis of dedifferentiated regions revealed cytokeratin showed multifocal expression. Vimentin and CD34 were abnormal negative. This case was diagnosed as a MSFT with dedifferentiation. The patient was well after the operation, but, unfortunately, he had a recurrence one year later.Conclusion: Pelvic cavity malignant solitary fibrous tumor is a rare tumor that is in frequently dedifferentiated and exhibiting cytokeratin expression. The diagnosis of this type of tumor can be confusing, and it should be distinguished from Synovial Sarcoma, Liposarcoma, and other malignant tumors. The expression of cytokeratin and the absence of vimentin and CD34 are pitfalls to diagnosis. In this case, there was still a high degree of malignancy despite the small size of the tumor. Clinical-image-pathological multidisciplinary analysis has a great effect on diagnosis and therapy of diseases. This case is a cautionary tale for surgeons and pathologists.