AB 34. Solitary fibrous tumor with focal malignant transformation. Description of a rare case

Background: Solitary fibrous tumor SFT is a rare mesenchymatogenic neoplasm, with intermediate malignant potential, usually localized in pleura. Malignant transformation observed at 23% of intrathoracic SFT. We present the unusual case of a 62-year-old patient presented to our hospital with a large SFT of the lung.
Patients and methods: We received for frozen sections and paraffinembedded (permanent) sections a lobulated, circumscribed, encapsulated tumour, weighting 879 gr. and measuring 16 cm × 12.5 cm × 11 cm. The tumour was compact, with grayish cut surface and thick constitution. Histological sections of the tumor were studied with conventional hematoxyline staining and immunohistochemically.
Results: Histologically observed mild-moderate cellularity neoplasm, composed of relatively uniform spindle cells with mild atypia and rare mitoses. Between cells inserted varying thickness collagen fibers and vascular formations with hemangiopericytomatous morphology. Focally, in central position, cellularity was increased with high nuclear atypia, mitoses >4/10 HPFs and necrosis. Immunophenotype of cells was: CD 34+, Bcl-2+, Vimentin+, CD 99-, SMA-, Desmin-, S-100, CK 8/18-, AE1/AE3-, EMA-, CD 117-, Ki-67: 10%. Solitary fibrous tumor must be differentiated from various spindle cell neoplasms including: Hemangiopericytoma, synovial sarcoma dermatofibrosarcoma protuberans, leiomyosarcoma, liposarcoma, and malignant schwannoma. The diagnosis of intraparenchymal solitary fibrous tumor of the lung with focal malignant transformation, was confirmed and based on morphology, immunophenotype and histologic criteria of malignancy.
Conclusions: The SFT can present malignant biological behavior with local recurrence or metastasis. According to the histological criteria of malignancy which proposed by Vallat-Decouvelaere et al.. Tumors with nuclear atypia, areas with increased cellularity, necrosis, tumor size >10 cm and mitoses >4/10 HPFs, can exhibit malignant behavior. The risk of local recurrence and metastasis is high even in so-called “benign” tumours after a long period of time. The treatment of choice is complete resection followed by extended follow-up surveillance.