International Journal of Histopathological Interpretation

: 2018  |  Volume : 7  |  Issue : 2  |  Page : 22--25

Solitary fibrous tumor of the pelvis: A case report

Kusum D Jashnani1, Jyothi B Shetty1, Yi Ching Ling2,  
1 Department of Pathology, TN Medical College and BYL Nair Charitable Hospital, Mumbai, India
2 Department of Obstetrics and Gynecology, TN Medical College and BYL Nair Charitable Hospital, Mumbai, India

Correspondence Address:
Jyothi B Shetty
B-2, Anand Bhavan, Lal Chimney Compound, Dr A. L. Nair Road, Mumbai 400011.


Solitary fibrous tumor (SFT) is a rare mesenchymal neoplasm most commonly seen in the pleura. Rarely they can occur at extrapleural sites. SFT of the pelvis is rare with very few cases reported in the literature. We report a case of a 35-year-old female who presented with complaints of pain in abdomen for the last 1 year. Computed tomography revealed a large mass lesion in the pelvis measuring 15.9 × 12 × 13.8 cm extending up to the L4-L5 level. Bilateral ovaries were not seen separately. Histopathological examination of the resected specimen revealed an SFT.

How to cite this article:
Jashnani KD, Shetty JB, Ling YC. Solitary fibrous tumor of the pelvis: A case report.Int J Histopathol Interpret 2018;7:22-25

How to cite this URL:
Jashnani KD, Shetty JB, Ling YC. Solitary fibrous tumor of the pelvis: A case report. Int J Histopathol Interpret [serial online] 2018 [cited 2022 Oct 7 ];7:22-25
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Full Text


Solitary fibrous tumors (SFTs) are rare mesenchymal neoplasms, first described by Klemperer and Rabin in 1992.[1] The WHO classification (2013) classifies them as tumors with intermediate malignancy.[2] Prior to this classification, SFT and hemangiopericytoma were regarded as separate entities. After the classification, they are considered as one entity.[3] This entity is known by various synonyms, viz., benign mesothelioma, pleural fibroma, localized fibroma, etc. Most of the SFTs are benign (78–88%) and 12–22% are malignant.[4] Histological predictors of aggressive behavior are high cellularity, high mitosis (>4/10 HPF), atypia, tumor necrosis, and infiltrative margins.[3]

 Case Report

A 35-year-old female complained of pain in abdomen since 1 year. Computed tomography abdomen revealed a large mass lesion in the pelvis measuring 15.9 × 12 × 13.8 cm extending up to the L4-L5 level. The mass was abutting the sigmoid colon and rectum anteriorly. Bilateral ovaries were not seen separately. The patient underwent surgery and the mass was resected.

Gross examination revealed a well-circumscribed and well-encapsulated mass measuring about 16 × 12.5 × 13 cm [Figure 1]. The mass was nodular externally and the cut section was pinkish white, firm without any areas of necrosis. Focal areas of calcification were seen [Figure 2]. The ovary measured about 4 × 2.5 × 0.8 cm and was seen attached to the mass by delicate fibrous strands. The cut section of the ovary showed multiple tiny cysts, largest measuring about 0.8 × 0.8 cm.{Figure 1} {Figure 2}

Histological examination of the mass revealed a tumor with patternless pattern [Figure 3]a. There were hyper- and hypocellular areas of spindle-shaped cells dispersed in a background of thin ropy collagen [Figure 3]b. Prominent hemangiopericytomatous vessels were seen in the background [Figure 3]c. Some of these vessels were hyalinized [Figure 3]d. Mitotis was not prominent. Immunohistochemical analysis showed a strong positivity for Bcl2 [Figure 4]a and CD34 [Figure 4]b and negative for CK, S100, Desmin, and C-kit. Based on these results, histopathological diagnosis of “solitary fibrous tumor of the pelvis” was offered.{Figure 3} {Figure 4}


SFT has been described rarely in extrapleural sites such as orbit, nasal cavity, salivary glands, upper respiratory tract, thyroid, peritoneum, pelvis, and genitourinary tract.[5] Extrapleural SFTs are uncommon with less than 100 cases reported in the literature.[6],[7] There is no gender predilection; however, this tumor primarily affects the middle aged to elderly individuals.[7] Though thought to be rare, in the last few years, the number of extrapleural SFTs reported have increased as 20 years back these tumors were diagnosed as hemangiopericytomas.[8]

Patients may be asymptomatic or may present with abdominal pain, fullness, or symptoms related to pressure effects.[6] Occasionally, some patients present with hypoglycemia as a part of paraneoplastic syndrome which is termed as Doege–Potter syndrome.[2] Due to these non-specific symptoms, the rarity of the tumor, and also non-specific imaging features such as necrosis, myxoid change, hemorrhage, and cystic change, it often poses a diagnostic difficulty.[7],[9]

Histological examination of this tumor followed by immunohistochemical studies helps in confirming the diagnosis. These tumors exhibit a classical pattern which is described as patternless comprising of spindle cells against a background of ropy collagen.[8] Immunohistochemically positive CD34 and Bcl2 are characteristics of SFT. CD34 is positive in 95–100% of cases.[3] SFTs are generally negative for S100, CK, SMA, desmin, and c-kit. These markers thus help in differentiating SFTs from other spindle cell tumors which are its differential diagnosis such as leiomyoma, angiomyolipoma, inflammatory myofibroblastic tumors, and gastrointestinal stromal tumors.[5] Criteria for malignancy include high cellularity, tumor necrosis, nuclear pleomorphism, and mitotic activity more than 4 per 10 high power fields.[8] None of these was seen in the present case.

Dedifferentiation is a poor prognostic factor in SFT wherein there is a sudden transition to a high grade sarcoma in addition to typical benign features of the tumor. Immunohistochemically, there is expression of p53 and loss of CD34 in the dedifferentiated areas.[3] Though mostly it follows a favorable course, SFT is notoriously difficult for prognostication because of its tendency for presentation with late relapse or metastases in 10–40% of cases.[10]

The main stay of treatment in SFT is surgical resection with negative margins. Those showing malignant features histologically or cannot be completely excised respond to radiation and/or chemotherapy.[1] The recurrence rate in SFTs is very low; hence, the use of adjuvant radiation and chemotherapy in malignant SFT is controversial.[4]


SFT is a rare mesenchymal tumor which can be seen in extrapleural sites. Histological findings and immunohistochemistry help in the diagnosis of this tumor which does not have specific symptoms or any specific imaging findings. Though commonly a benign tumor, one has to be aware of its malignant potential in a small percentage of cases. Its unpredictable behavior prompts several proposed schemes incorporating age, size, mitosis, and/or necrosis as factors for risk stratification. Hence, more studies need to be done on this entity with follow-up of the patients which will help in designing an appropriate management protocol for this tumor. A long-term follow-up is recommended for these patients for future recurrence. Our patient was not given post-operative radiation or chemotherapy as the SFT was benign on histomorphology. She has been advised regular follow-up, and till 9 months after surgery, she is free of disease and without any recurrence.

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1Ge W, Yu DC, Chen G and Ding YT. Clinical analysis of 47 cases of solitary fibrous tumour. Oncol Lett 2016;12:2475-80.
2Ouladan S, Trautmann M, Orouji E, Hartmann W, Huss S, Büttner R, et al. Differential diagnosis of solitary fibrous tumors: A study of 454 soft tissue tumors indicating the diagnostic value of nuclear STAT6 relocation and ALDH1 expression combined with in situ proximity ligation assay. Int J Oncol 2015;46:2595-605.
3Geramizadeh B, Marzban M, Churg A. Role of immunohistochemistry in the diagnosis of solitary fibrous tumor, a review. Iran J Pathol 2016;11:195-203.
4Umadevi KR, Srivani J, Ezhilvizhi A. Extra pleural solitary fibrous tumor—A rare case report. IJSR 2014;3:290-1.
5Zhou Y, Chu Xi, Yi Ye, Tong L, Dai Y. Malignant solitary fibrous tumor in retroperitoneum—A case report and literature review. Medicine 2017;96:1-4.
6Kim MY, Jeon S, Choi SD, Nam KH, Sunwoo JG, Lee JH. A case of solitary fibrous tumor in the pelvis presenting massive hemorrhage during surgery. Obstet Gynecol Sci 2015;58:73-6.
7Boe J, Chimpiri AR, Liu CZ. Solitary fibrous tumor originating in the pelvis: A case report. J Radiol Case Rep 2010;4:21-8.
8Pata F, Orsini V, Lucisano AM, Pafundi DP, Sacco R. Solitary fibrous tumor of the pelvis: An uncommon soft-tissue tumor. A case report. Ann Ital Chir 2010;81:457-60.
9Fursevich D, Derrick E, O’Dell MC, Vuyyuru S, Burt J. Solitary fibrous tumor of the kidney: A case report and literature review. Cureus 2016;8:e490.
10Huang SC, Huang HY. Solitary fibrous tumor: An evolving and unifying entity with unsettled issues. Histol Histopathol 2019;34:313-34.