Indian Journal of Pathology and Microbiology

: 2014  |  Volume : 57  |  Issue : 4  |  Page : 652--653

Malignant Ossifying Fibromyxoid Tumors: A report of two rare cases displaying retained INI1/SMARCB1 expression

Bharat Rekhi, Swati Thorat, Gopal Parikh, Nirmala A Jambhekar 
 Department of Pathology, Tata Memorial Hospital, Parel, Mumbai, India

Correspondence Address:
Dr. Bharat Rekhi
Professor/ Pathologist, Department of Pathology, 8th Floor, Annex Building, Tata Memorial Hospital, Dr. E.B. Road, Parel, Mumbai

How to cite this article:
Rekhi B, Thorat S, Parikh G, Jambhekar NA. Malignant Ossifying Fibromyxoid Tumors: A report of two rare cases displaying retained INI1/SMARCB1 expression.Indian J Pathol Microbiol 2014;57:652-653

How to cite this URL:
Rekhi B, Thorat S, Parikh G, Jambhekar NA. Malignant Ossifying Fibromyxoid Tumors: A report of two rare cases displaying retained INI1/SMARCB1 expression. Indian J Pathol Microbiol [serial online] 2014 [cited 2022 Jul 1 ];57:652-653
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Ossifying fibromyxoid tumor of soft parts (OFMT) is a rare musculoskeletal tumor with an uncertain line of differentiation and found to display incomplete schwannian and/or cartilaginous differentiation. It mostly arises in the subcutaneous tissue or skeletal muscles of the extremities, but has also been reported at other sites, such as the trunk, head and neck, mediastinum and retroperitoneum. [1]

OFMTs display characteristic histopathological features and are classified as "typical", "atypical" or "malignant" OFMTs, based on their size, nuclear grade, cellularity, and mitotic activity. [2],[3],[4],[5] Malignant OFMTs (MOFMTs) are extremely rare.

Integrase interactor1 or INI1/hSNF5/SMARCB1/BAF47, a ubiquitously expressed tumor suppressor gene located on the chromosome 22q11.2, is a member of the SWI/SWF chromatin-remodelling complex. Deletions, mutations, other somatic alterations in INI1/hSNF5 gene have been detected in certain soft tissue tumors, such as malignant rhabdoid tumor, including extrarenal rhabdoid tumor and in other sarcomas, most commonly, epithelioid sarcomas. [6] Recent studies have shown "mosaic pattern" of loss of INI1/SMARCB1 in certain OFMTs, including in MOFMTs. [4]

A 60 year-old-lady presented with a recurrent tumor around her knee joint. Eight years earlier, she had undergone wide-excision for the same tumor.

Another case occurred in a 26 year-old-male presenting with a swelling on the dorsum of his foot that measured 4.6 × 1.3 × 1.7 cm 3 . Imaging revealed well-defined enhancing soft tissue mass on the dorsolateral aspect of his foot along the extensor tendon, infiltrating into base of his fourth metatarsal bone and into adjacent subcutaneous tissues.

Histopathologically, both the tumors were relatively circumscribed and multinodular with peripheral thickened collagen and a shell of lamellar bone, more completely seen in the first tumor. Both tumors were composed of polygonal cells forming clusters and trabeculae amidst fibromyxoid stroma. Both tumors were focally infiltrative and displayed areas with high cellularity, high nuclear atypia and mitoses 2-3/10 high power fields. Immunohistochemically (IHC), both tumors expressed S100-P (nuclear and cytoplasmic) and INI1/SMARCB1. Ki-67 highlighted 30-40% nuclei in the malignant areas in the first tumor. AE1/AE3, epithelial membrane antigen (EMA), cytokeratin (CK), smooth muscle actin (SMA), desmin and CD34 were negative [Figure 1].{Figure 1}

OFMTs form a wide histopathological spectrum. [1],[2],[3],[4],[5] Despite substantial number of reported OFMTs; MOFMTs are fairly uncommon, including no report from our subcontinent. In two different studies from western literature, these constituted as 7% and 17.6% of the OFMTs, respectively. [2],[3]

These tumors commonly afflict deeper soft tissues of extremities, as noted in both the present cases. Histopathologically, the differential diagnoses included synovial sarcoma (SS), malignant peripheral nerve sheath tumor, sclerosing epithelioid fibrosarcoma, and fibroosseous tumor of digits. Lack of epithelial marker (CK, EMA and AE1/AE3) expression and presence of aforementioned histopathological features ruled out a SS. Similarly key histopathological features and immunohistochemical profile militated against other differentials. The diagnostic difficulty within OFMTs is to identify malignant counterparts, as these are more commonly associated with recurrences and metastasis.

It has been observed that hypercellularity and nucleomegaly that characterize malignant OFMT are usually readily apparent even at scanning magnification in form of a distinct hypercellular area, as noted in the present cases. Criteria for malignancy are mitotic figures more than 2/50 hpf, as noted in both the cases that recurred. [3] The existence of fully malignant OFMT is controversial. Lately, a "mosaic pattern", in the form of loss of INI1 expression in 30% to 60% lesional cells, was noted in 74% OFMTs. [4] Thereafter, no other study has explored INI1 expression in OFMTs. Contrastingly, we observed intact INI1 expression in both the study tumors. Recently, Grahm et al. [5] documented PHF1 rearrangements in 49% OFMTs, including 52% malignant ones. In conclusion, MOFMTs are extremely rare tumors that require analysis of key histopathological features and optimal IHC markers for their correct diagnosis. MOFMTs seem to develop as a result of malignant transformation in an otherwise OFMT. In our experience, these did not exhibit loss of INI1. Documentation of additional such cases with INI1 results, including genetic analysis would further validate these observations and provide additional insights related to INI1 expression in MOFMTs.


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