868462 research-article2019 PAT0010.1177/2632010X19868462Clinical PathologyBarco et al Malignant Solitary Fibrous Tumour of the Clinical Pathology Volume 12: 1–4 Breast Mimicking a Benign Tumor © The Author(s) 2019 Article reuse guidelines: sagepub.com/journals-permissions Israel Barco1 , Clarisa González2, Elena Vallejo1, DOI: 10.1177/2632010X19868462 https://doi.org/10.1177/2632010X19868462 Antoni Pessarrodona3, Nuria Giménez4,5 and Antonio García-Fernández1 1BreastUnit, Department of Gynecology, University Hospital of Mútua Terrassa, University of Barcelona, Terrassa, Spain. 2Department of Pathology, University Hospital of Mútua Terrassa and Research Foundation Mútua Terrassa, University of Barcelona, Terrassa, Spain. 3Department of Gynecology, University Hospital of Mútua Terrassa, University of Barcelona, Terrassa, Spain. 4Research Unit, Research Foundation Mútua Terrassa, University of Barcelona, Terrassa, Spain. 5Laboratory of Toxicology, Universitat Autònoma de Barcelona, Barcelona, Spain. ABSTRACT: Solitary fibrous tumour (SFT) of the breast is exceedingly uncommon. Radiological assessment usually shows benign features. We report on a case of malignant SFT of the breast, while emphasizing the need for additional immunostains to reach a definitive diagnosis. Standard treatment consists of lesion removal with adequate margins. Keywords: Solitary fibrous tumours, breast, diagnosis, pathology, surgical, diagnostic imaging RECEIVED: May 28, 2019. ACCEPTED: June 18, 2019. Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this Type: Original Research article. Funding: The author(s) received no financial support for the research, authorship, and/or CORRESPONDING AUTHOR: Israel Barco, Breast Unit, Department of Gynecology, publication of this article. University Hospital of Mútua Terrassa, University of Barcelona, Plaça Dr. Robert 5, Terrassa 08221, Barcelona, Spain. Email: ibarco@mutuaterrassa.es Introduction Core-needle biopsy showed a hypercellular spindle-cell Solitary fibrous tumour (SFT) is an uncommon mesenchymal tumour with epithelioid cells, overall low cytological atypia, neoplasm, most often found in the pleura. Other ubiquitous and 1 mitosis per 10 high-power field (HPF). The following sites have also been reported, although extra-thoracic lesions immunophenotype was disclosed: positive for vimentin and seem scarce. Breast SFT seems even more uncommon, with CD34; negative for desmin, beta-catenin, P63, keratins, and just a few cases reported in the literature. breast hormone receptors. Proliferative marker Ki67 was 10%. Age at presentation is variable, with a range between 49 and Such description was consistent with a mesenchymal epithe- 81 years. It usually presents as a single, large, painless, slow- lioid and fusocellular lesion lacking enough features of malig- growing lump. Radiological features resemble those of benign nancy. Myofibroblastoma was the initial diagnosis. Nevertheless, lesions. Specimens from core-needle biopsy often are incon- whole lesion removal was suggested to reach a definite histo- clusive, showing pathologic features that overlap with other logic assessment. mesenchymal lesions, such as myofibroblastoma (MFB). A The surgical specimen consisted of a well-defined mass definitive diagnosis can be better reached after complete lesion showing a fine fibrous capsule with focally infiltrative margins. removal. Solitary fibrous tumour occurring in the breast is usu- Microscopic assessment showed a hypercellular lesion with ally benign. We report on a case of malignant SFT of the breast focal deposition of dense hyaline bands, myxoid change, and and emphasize the need for additional immunostains to get a focal necrosis (10%). Uniform, round epithelioid spindle cells definitive diagnosis (STAT6). with scant cytoplasm were seen displaying an alveolar-like growth pattern, with nuclear pleomorphism, a mitotic index of Case Report 15/10 HPF, along with giant multinucleated stromal cells and A 72-year-old woman attended our outpatient clinic after thick-walled vessels arranged in a ‘stag horn’ pattern (Figure 2A noticing a lump in her right breast for about 2 months, which and B). Immunophenotype was as follows: positive for vimen- had been growing steadily. She had had a previous surgery for tin, CD34, BCL2, CD99, STAT6 (diffuse and strong nuclear fibroadenoma removal in the same breast 30 years ago. Also, immunoreactivity), and TLE1; CD10 and synaptophysin she had gone through a total hysterectomy for multiple fibroids (scattered positivity); negative for desmin, beta-catenin P63, at the age of 48. P40, keratins (CK AE1-3, CK5/6, 34B-E12), S100, CD31, Upon examination, a palpable lump of 2-3 cm located at the myosin heavy chain, and hormone receptors. The proliferation inner quadrants of her right breast was found, associated to marker Ki67 was 20% cell positive. mild skin retraction. No pain, nipple discharge, or enlarged Thus, evidence of a hypercellular lesion with nuclear pleo- regional lymph nodes were present. Mammography and ultra- morfism, high mitotic index, and infiltrative margins associated sound showed a 27 mm ×13 mm, well-defined lobulated nod- with strong nuclear STAT6 immunostain led to the final ule causing skin retraction (BiRads 4C) (Figure 1A and B). histologic diagnosis of malignant SFT (Figure 3). According Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage). 2 Clinical Pathology  Figure 1. (A) Mammography. (B) Ultrasound. Figure 3. Positive immunohistochemical staining for STAT6 (intense nuclear expression). Well-defined tumour associated with perilesional fatty tissue invasion (×200). to Demicco et al’s1 refined stratification model, this case fitted into the intermediate risk class for distant metastasis, and the patient was instructed to attend regular controls every 3-4 months (Figure 3). No adjuvant therapy was indicated, since there is no evi- dence that neither radiotherapy nor chemotherapy actually add any benefit. The lesion recurred after 18 months, leading to mastectomy to warrant negative margins. This report was done in accordance with the Review Board and Ethics Committee of Mutua Terrassa. Discussion Figure 2. H&E stained sections of the surgical specimen. (A) Focal Solitary fibrous tumour is a rare spindle-cell fibroblastic infiltrative margin extending into the perilesional fatty tissue (H&E ×400). tumour usually arising in the pleura. Other reported locations (B) Hypercellular lesion with an alveolar-type growth pattern. Hemangiopericytoma-like stag-horn vascular spaces, and giant include the upper respiratory tract, mediastinum, head and multinucleated stromal cells showing pleomorphic nuclei, together with neck, soft tissue elsewhere, central nervous system (CNS), kid- collagenous matrix, prominent mitoses, and focal necrosis (H&E ×400). ney, and breast.2-5 There are very few cases described in this latter location,6-10 and most of them are benign and limited to Barco et al 3 Table 1. Differential diagnosis in case of possible solitary fibrous at presentation, distant metastases, and high histologic grade tumour. were independent adverse prognostic factors predicting dis- Benign lesions Malignant lesions ease-free survival and overall survival. Although SFT cases usually follow a benign course, a close follow-up is recom- Myofibroblastoma Monophasic synovial sarcoma Spindle-cell lipoma Desmoid-type fibromatosis mended since cases of recurrent tumour (as in our case) or dis- Leiomyoma Low-grade, spindle-cell, fibromatosis-like tant relapse have indeed been reported. Inflammatory metaplastic carcinoma myofibroblastic Dermatofibrosarcoma tumour/inflammatory Leiomyosarcoma Conclusion pseudo-tumour Fibrosarcoma/malignant fibrous Solitary fibrous tumour of the breast is exceedingly uncom- histiocytoma Low- or high-grade myofibroblastic mon. Radiological assessment usually shows benign features. sarcoma Histology may show overlapping characteristics with other Malignant peripheral nerve sheath tumour conditions. Use of STAT6 immunostain is helpful to achieve a diagnosis. Standard treatment consists of lesion removal with adequate margins. the female gender. A malignant variant has also been reported but is even more uncommon.11 Acknowledgements Although SFT can occur at any age, it is mostly seen in The authors wish to express their gratitude to Ms Patricia patients in their 50s. It usually presents as a single, painless, and Vigués for correcting the manuscript and Dr Manel Fraile slow-growing lump that shows benign features at the radio- from Nuclear Medicine Department, University Hospital of logical work-up, such well-defined margins and smooth echo- Mútua Terrassa, for providing support and advice. structure. Because imaging features are mostly non-specific, Author Contributions the final diagnosis is based on histologic examination. IB contributed to fostering of the case study, literature review, On histology, STF shows overlapping characteristics with attending the patient, writing the manuscript, and is guaran- other mesenchymal lesions, such as MFB. The final diagnosis tor of the paper. CG contributed to the histological diagno- of breast SFT is challenging because there is much variability sis, literature review, and critical revision of the manuscript. concerning its cellular, extracellular, and vascular components, EV, AP, and AG-F contributed to attending the patient, lit- and because it can mimic other spindle-cell tumours. Complete erature review, and critical revision of the manuscript. NG removal of the lesion is often required to reach a final diagnosis, contributed to fostering of the case study, literature review, since potential sampling errors can occur if only needle biopsy and writing the manuscript. All authors reviewed the final is performed. manuscript. According to Magro et al,12 several conditions can be included in the differential diagnosis (Table 1). However, in Informed Consent most cases, a differential diagnosis should be established Informed consent was obtained from the patient presented. between breast SFT and MFB, the latter featuring myoid cells with eosinophilic cytoplasm, nearly no myofibroblastic traits, ORCID iD scant hemangiopericytoma-like pattern, and positive muscle Israel Barco https://orcid.org/0000-0003-3520-8736 immunostains (desmin, actin). There is increasing evidence that MFB and other associated benign tumours are linked to loss of material in chromosome References 13, whereas SFT is not.5,13 Recently, a new fusion gene, NAB2- 1. Demicco EG, Wagner MJ, Maki RG, et al. Risk assessment in solitary fibrous tumors: validation and refinement of a risk stratification model. Mod Pathol. STAT6, has been suggested as a specific diagnostic marker for 2017;30:1433-1442. SFT.14 Interestingly, in our case, the final diagnosis could only 2. Fletcher CDM, Gibbs A. Solitary fibrous tumour. 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