|Year : 2020 | Volume
| Issue : 1 | Page : 35-38
Myoepithelial carcinoma with heterologous differentiation presenting as exophytic mass on forearm: A rare case
Vedita M Bobde, Satish B Helwatkar, Waman K Raut
Department of Pathology, Government Medical College, Nagpur, Maharashtra, India
|Date of Submission||01-Apr-2020|
|Date of Acceptance||04-Jun-2020|
|Date of Web Publication||08-Jul-2020|
Dr. Vedita M Bobde
Patrakar Colony, Vasantnagar, Near Dikshabhoomi, Nagpur, Maharashtra,
Source of Support: None, Conflict of Interest: None
Myoepithelial tumors of soft tissue origin are rarely seen unlike their salivary counterpart. Myoepithelial carcinomas are even rarer, and only 15% show heterologous differentiation. They are usually misdiagnosed as skin malignancies because of their subcutaneous location. No age-group is exempted but malignant counterparts are more common in children. Surgery is the mainstay of treatment, and early diagnosis is desirable to avoid metastatic spread. Heterologous elements, if not represented in biopsy, lead to misdiagnosis. Immunohistochemistry is helpful in difficult to diagnose cases.
Keywords: Immunohistochemistry, myoepithelial carcinoma, myoepithelial carcinoma with heterologous differentiation
|How to cite this article:|
Bobde VM, Helwatkar SB, Raut WK. Myoepithelial carcinoma with heterologous differentiation presenting as exophytic mass on forearm: A rare case. J Curr Oncol 2020;3:35-8
| Introduction|| |
Myoepithelial tumors of soft tissue origin are uncommon and are placed in tumors of uncertain differentiation in the fourth edition of World Health Organization (WHO) Classification of Soft Tissue Tumors. On clinical examination, they are usually misdiagnosed as skin epithelial or adnexal tumors because of their subcutaneous location when involving extremities. They are morphologically and immunophenotypically similar to salivary myoepithelial tumors but have uncommon occurrence. They are classified as myoepithelioma, myoepithelial carcinoma, mixed tumor not otherwise specified, and malignant mixed tumor. They are synonymous with ectomesenchymal chondromyxoid tumor and parachordoma as per WHO classification. They show wide age distribution with a peak in young adults and equal sex distribution. Myoepithelial carcinomas predominate in pediatric population. They usually present as palpable painless masses on upper and lower limb girdles and are less common on trunk, head, neck, bone, or visceral organs. They arise commonly in subcutaneous location than in deep soft tissue. Malignant myoepithelial tumors are rare, and only 15% show heterologous differentiation. Very few cases of myoepithelial carcinoma of soft tissue have been reported so far because of rarity of the lesion. We report a similar case in a 65-year-old male patient on the forearm, which was initially misdiagnosed on clinical examination and incisional biopsy as squamous cell carcinoma.
| Case Report|| |
A 65-year-old man presented with rapidly enlarging exophytic mass on the lateral aspect of left forearm since 6 months. The growth was having completely ulcerated necrotic surface. On examination, growth measured 6 × 5 × 4 cm sessile mass not fixed to the underlying bone [Figure 1]. X-ray showed a well-circumscribed soft tissue mass, and the underlying bones were free [Figure 2]. Wide local excision was followed after an incisional biopsy diagnosis of squamous cell carcinoma at other center. We received exophytic growth with narrow rim of normal skin on the lower side measuring 6 × 5 × 4 cm, with ulcerated and necrotic surface. Mass was firm in consistency, gray white solid with glistening myxoid areas on the cut surface. Growth showed pushing margins unlike others quoted in literature, which showed infiltrative margins, and the base of the mass was free from tumor infiltration [Figure 3].
|Figure 1: Clinical photograph. Exophytic mass on lateral aspect of left forearm showing ulcerated surface|
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|Figure 2: X-ray. Anteroposterior and lateral view showing soft tissue mass with underlying bones free from tumor infiltration. A is anteroposterior and B is lateral view of Xray|
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|Figure 3: Gross specimen. (A) External surface completely ulcerated necrotic. (B) Cut surface showing variegated gray-white glistening areas|
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| Microscopy|| |
The growth showed well-circumscribed tumor with pushing margins not infiltrating the underlying muscles with heterogenous areas. Tumor cells were round to oval to short spindle arranged in sheets, cords, and nests having eosinophilic to clear cytoplasm, surrounded by predominantly chondromyxoid stroma. Foci of osteoid differentiation, adipocytic differentiation, and squamous differentiation were also seen. Tumor showed large areas of necrosis and hemorrhages. Plenty of atypical mitotic figures variable in numbers, in some areas 8–10/10 high power field (hpf) were seen. Bizarre tumor giant cells were abundant. Very focal ductal differentiation was appreciated [Figure 4]. Incisional biopsy did not represent all the heterologous areas, and it was misinterpreted as squamous cell carcinoma. Immunohistochemistry was done for confirmation [Figure 5]. Tumor was positive for cytokeratin, S100, and epithelial membrane antigen (EMA), and integrase interactor 1 (INI) was retained. INI is lost in subset of cases of myoepithelioma. Similar immunohistochemical features were seen in a study by Rekhi et al. Tumor was negative for myoglobin, desmin, CD99, and neuron-specific enolase.
|Figure 4: Microscopy (hematoxylin and eosin stain, ×400). (A) Bizarre multinucleated cells in osteoid background. (B) Adipocytic differentiation with sheets of myoepithelial cells in between. (C) Round to oval cells with hyperchromatic nuclei in sheets and cords surrounded by fibrocollagenous stroma. (D) Squamous differentiation in myoepithelial cells|
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|Figure 5: Immunohistochemistry showing S100, CK, and EMA positivity. INI is retained (×400)|
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| Discussion|| |
Myoepithelial tumors of soft tissue are rare entities, and 20%–30% show malignant change. Hornick and Fletcher studied 101 cases of soft tissue myoepithelial tumors, found in the age range of 3–83 years with average age of 38 years, mostly seen in the extremities and limb girdles. Similar site of tumor was described in a 17-year-old Japanese female patient, who later on presented and succumbed with lung metastasis. Average age of distribution is 49 years as quoted by Chamberlain et al. in their series of 24 cases of myoepithelial carcinoma. Heterologous elements in the form of chondrosarcoma, liposarcoma, osteogenic sarcoma, rhabdomyosarcoma, and squamous cell carcinoma are seen in only 15% cases. Depending on which element predominates in microscopy, differential diagnosis ranges from extraskeletal myxoid chondrosarcoma, ossifying fibromyxoid tumor, epithelioid schwannoma, metastatic carcinoma, metastatic melanoma, and epithelioid sarcoma. Our case also showed multiple heterologous elements in the form of chondrosarcoma, squamous metaplasia, liposarcoma, and tumor-induced osteoid. Owing to incomplete representation of various heterologous elements, Tru-Cut biopsies and incisional biopsies can be diagnosed as any of the differentials stated above. S100 positivity rules out metastatic carcinoma, and cytokeratin positivity excludes myxoid chondrosarcoma. Other myoepithelial markers, calponin, glial fibrillary acidic protein (GFAP), smooth muscle actin (SMA), and P63 are positive in subset of cases only. However, typical histomorphology is sufficient to suggest myoepithelial origin in certain cases. Tumors were treated primarily with surgical resection.
Myoepithelial carcinoma metastasizes in 40%–50% cases, commonly to lungs, lymph nodes, bone, and soft tissue.
| Conclusion|| |
Myoepithelial carcinomas though rare should be kept in differential diagnosis while reporting on exophytic masses on extremities. Histopathological confirmation is a must after complete excision to confirm various heterologous elements that may define the biological behavior of the tumor.
Declaration of Patient Consent
The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.
We are thankful to the head of the Department of Pathology, Armed Forces Medical College, Pune, Maharashtra, India, and their teaching and technical staff for providing the immunohistochemistry of this case.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5]