---------------------------- 2021 Platform Presentation Winner (shared) --------------------------

[560] Solitary Fibrous Tumors of the Female Genital Tract: A Detailed Morphologic Study of 27 Cases

Kyle Devins, Sabrina Croce, Eike-Christian Burandt, Jennifer Bennett, Anna Pesci, Gian Franco Zannoni, G. Pétur Nielsen, Robert Young, Esther Oliva.


Background: Solitary fibrous tumors (SFT) are uncommon mesenchymal tumors and most examples in the female genital tract described to date have been in the vulva. They may be mistaken for a variety of tumors depending upon their location. Herein we report the largest series of gynecologic (GYN) SFT to date focusing on variant morphology and drawing attention to non-vulvar locations.

Design: Cases were identified from the departmental pathology files of participating institutions as well as our consultation files. All available H&E and immunohistochemical slides were reviewed.

Results: 27 primary GYN tract SFT were identified, involving the vulva (n=7), vagina (n=2), cervix (n=2), corpus (n=6), fallopian tube/peritubal soft tissue (n=5), and ovary (n=5). An average of 10 H&E slides were reviewed (range 2 – 51). Size of tumors ranged from 1.5 – 30 (mean = 9.8) cm. Upper GYN-SFT tended to be larger (mean 12.4 vs. 5.4 cm, p = 0.05) than lower GYN-SFT. Based on soft tissue classification of these tumors, 21 were classic; 5 were malignant based on the presence of ≥4 mitoses/10 hpf +/- infiltrative borders; and one showed dedifferentiation with pleomorphic and undifferentiated spindle cell components. Upper GYN-SFT were typically more cellular than lower GYN-SFT. Tumors often demonstrated variant morphologies comprising 5 to >50% of tumor including microcysts (n=9), myxoid background (n=7), cords (n=6), fascicular growth (n=5), multinucleated cells (n=5), adipocytic differentiation (n=2), nuclear palisading (n=2), and dilated anastomosing vascular channels (n=2). More than one of these features was often seen within the same tumor. Additional features not previously reported included entrapped thick-walled vessels (n=7), “alveolar” edema (n=7), and epithelioid cells with pseudotubular formation (n=1), although these findings were present only focally. STAT6 was positive in 25/25 tumors tested. Two older cases with classic histologic features (vagina and vulva) had no blocks available for staining. Follow-up was available in two patients with malignant SFT; both were alive with recurrent intra-abdominal disease after 12 and 47 months. Time to recurrence was 12 and 17 months respectively.

Conclusions: SFT in the GYN tract demonstrate a wide range of variant morphologies and occur in diverse sites in addition to the vulva. Awareness of these features may improve recognition of these rare tumors which have likely been overlooked when arising at unusual sites such as the ovary.