|Year : 2015 | Volume
| Issue : 3 | Page : 647
Primary myoepithelial carcinoma of rib bone: Morphology, immunohistochemical evaluation and diagnostic dilemma in an unusual case
Pramod Biradar1, Santosh Menon1, Asawari Patil1, George Karimundakal2, Nirmala Jambhekar1
1 Department of Pathology, Tata Memorial Hospital, Mumbai, India
2 Department of Thoracic Surgery, Tata Memorial Hospital, Mumbai, India
|Date of Web Publication||9-Oct-2015|
Dr. Santosh Menon
Department of Pathology,Tata Memorial Centre, Parel, Mumbai - 400 012, Maharashtra
Source of Support: None, Conflict of Interest: None
Myoepithelial tumors are most commonly seen as salivary gland tumors. Tumors of similar morphology and nomenclature are also seen rarely in soft tissue, skin, lungs and breast. Bone is an uncommon anatomical site for occurrence of myoepithelial tumors. Histologically, they have variable admixture of epithelial elements in a gamut of patterns with myxoid matricial background. Most of these are benign with very anecdotal reports of malignant counterpart, myoepithelial carcinoma. Herein we describe an extremely rare case of a malignant myoepithelial tumor arising from the rib which owing to unusual location and immunohistochemical profile was diagnostically challenging.
Keywords: Carcinoma, immunohistochemistry, myoepithelial, rib
|How to cite this article:|
Biradar P, Menon S, Patil A, Karimundakal G, Jambhekar N. Primary myoepithelial carcinoma of rib bone: Morphology, immunohistochemical evaluation and diagnostic dilemma in an unusual case. J Can Res Ther 2015;11:647
|How to cite this URL:|
Biradar P, Menon S, Patil A, Karimundakal G, Jambhekar N. Primary myoepithelial carcinoma of rib bone: Morphology, immunohistochemical evaluation and diagnostic dilemma in an unusual case. J Can Res Ther [serial online] 2015 [cited 2020 Jul 11];11:647. Available from: http://www.cancerjournal.net/text.asp?2015/11/3/647/136035
| > Introduction|| |
Myoepithelial tumors usually arise from myoepithelial cells around the acini and ducts of salivary glands. Apart from salivary glands they have also been reported to occur in the breast, soft tissue, skin, nasopharynx, sinonasal tract, larynx, and lung.  Myoepithelial tumors in these locations show histologic features similar to the mixed tumors and myoepitheliomas of salivary gland origin.  Unlike mixed tumors, myoepitheliomas lack obvious ductal differentiation. 
Criteria for malignancy in myoepithelial tumors of soft tissue have only recently been established and are essentially cytological, in contrast to the criteria used in salivary gland neoplasms. While most mixed tumor/myoepitheliomas of soft tissue have minimal or no atypia, myoepithelial carcinomas are characterized by epithelioid or spindled cells with vesicular or coarse chromatin, prominent, often large nucleoli, and nuclear pleomorphism.  Soft tissue myoepithelial carcinoma is a particularly rare tumor with around 50 cases reported so far. ,,, Due to their morphologic and immunophenotypic heterogeneity, these tumors may be mistaken for a variety of other soft tissue tumors when arising outside of the salivary glands.  Hence immunohistochemical stains are needed for confirmation. Recent studies have supported the hypothesis that soft tissue myoepithelial carcinomas are a distinct entity, not sharing the cytogenetic alterations typical of salivary gland myoepithelial carcinomas and ductal carcinomas of breast with myoepithelial differentiation. 
| > Case report|| |
A 48-year-old woman was referred to our institute with complaints of swelling over right scapular region diagnosed as metastatic adenocarcinoma. Whole body Positron Emission Tomography scan (PET-CT) showed a mass in the lateral wall of chest eroding into the underlying fifth rib. Rest of the body showed no other mass or obvious abnormalities.
CT-guided biopsy of the mass on histopathologic examination showed atypical cells against a myxoid background. In view of histomorphology, estrogen receptor (ER) and progesterone receptor (PR) positivity, it was reported as a case of metastatic adenocarcinoma with a possible primary in the breast. Bilateral digital mammogram and Magnetic Resonance Imaging (MRI) of breasts were performed and showed no evidence of dominant mass, architectural disturbance, or pleomorphic calcification in either breast.
Subsequently, surgical resection of the mass along with the involved rib was performed with wide margins. Grossly, the tumor was seen involving the inner cortex of the fifth rib, measuring 3 × 3 × 2 cm [Figure 1]a. On cut section the tumor showed a homogeneous, glistening surface with areas of hemorrhage. Histopathologic examination revealed a malignant tumor composed of cords of epithelioid and spindled cells arranged predominantly in a trabecular/reticular growth pattern. The neoplastic cells were separated by variably prominent myxoid stroma [Figure 1]b-d. The tumor had infiltrative margins and the bone was destroyed by tumor. All the resection margins were free. On immunohistochemistry (IHC), the tumor showed reactivity for myoepithelial markers p63, calponin, smooth muscle actin (SMA) and epithelial marker, epithelial membrane antigen (EMA); thus establishing a myoepithelial line of differentiation. The tumor was however negative for S-100 protein, Glial Fibrillary Acidic Protein (GFAP), cytokeratin cocktail (AE1/AE3), cytokeratin 7 (CK7) and cytokeratin 20 (CK20). It unusually expressed estrogen receptor (ER) and progesterone receptor (PR) [Figure 2].
|Figure 1: CT Thorax showing a mass present on the inner aspect of V rib and eroding into it (a). Histopathology showing lobular configuration of a myxoid tumor (b), H and E, magnification ×40). Higher power view showing cords and trabeculae of epithelial cells in a myxoid matrix reminiscent of a salivary gland tumor (c and d), H and E, magnification ×100 and ×200, respectively|
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|Figure 2: Immunohistochemistry (indirect immunoperoxidase method) in myoepithelial carcinoma. EMA and P63 positivity (a and b), magnification ×100. Calponin and estrogen receptor positivity (c and d), magnification ×100|
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In view of typical histomorphologic features and reactivity for epithelial and myoepithelial markers, it was diagnosed as a case of myoepithelial carcinoma of rib.
Myoepithelial tumors of soft tissue showing moderate or severe cytologic atypia (variably prominent nucleoli, vesicular or coarse chromatin, nuclear pleomorphism) behave aggressively with frequent recurrences and metastases and are accordingly classified as malignant.  Myoepithelial carcinoma have only recently been described in soft tissue and to date, around 50 cases have been reported in the literature. 
| > Discussion|| |
Myoepithelial tumors are equally common in males and females; occur in a wide age range with a peak in the third to fifth decades. Interestingly, myoepithelial tumors of soft tissue in children are much more likely to be malignant and aggressive than those in adults.  Nearly two-thirds of reported cases have arisen on the extremities (65%; 38% lower extremity and 27% upper extremity); the remainders have involved the head and neck region (16%), trunk (13%) and visceral soft tissue (6%). Approximately 60% of tumors are subcutaneous in origin, and 40% occur in deep soft tissue (intramuscular or subfascial). ,,, Grossly, most tumors are well circumscribed and described as nodular or lobulated. The cut surface is usually glistening, myxoid, or gelatinous.  Neoplastic myoepithelial cells can take on various morphological shapes, including epithelioid, spindle cell, clear cell, and plasmacytoid appearances. , Most tumors are heterogeneous, having an admixture of these cell types, as was seen in our case. Prominent chondromyxoid or hyalinized stroma is seen, and rarely foci of cartilaginous or osseous differentiation are noted.
Myoepithelial neoplasms have a somewhat variable immunophenotype, but often show reactivity for S-100 and/or GFAP. Therefore, to confirm myoepithelial differentiation in tumors of skin and soft tissue, expression of epithelial markers (keratin and/or EMA) as well as either S-100 or GFAP is required. In rare cases, expression of both epithelial and myogenic markers may be considered sufficient in the absence of S-100 or GFAP, if the tumor shows classic morphological features, as was seen in our case. 
Due to their myriad morphological features, differential diagnoses include metastatic carcinoma, metastatic malignant melanoma, high-grade extraskeletal myxoid chondrosarcoma (EMC), epithelioid malignant peripheral nerve sheath tumor (MPNST), and proximal-type epithelioid sarcoma. Metastatic carcinoma typically occurs in older patients and lacks the myxoid stroma and multinodular architecture typical of myoepithelial carcinoma. Further, immunoreactivity for S-100 protein, GFAP, and myogenic markers favors a diagnosis of myoepithelial carcinoma. Metastatic melanoma lacks the chondromyxoid or hyaline stroma typical of myoepithelial carcinoma and shows immunoreactivity for melan-A, HMB-45. High-grade EMC may occasionally show rhabdoid features, mimicking the plasmacytoid cells of some myoepithelial tumors.  However, EMC usually shows remarkable cytological uniformity. Although S-100 may be positive in a minority of EMC, they are uniformly negative for keratin, and GFAP reactivity is rare.  Histological features of epithelioid MPNST can closely mimic myoepithelial carcinoma. Epithelioid MPNST are strongly positive for S-100 and may express GFAP, and both epithelioid MPNST and myoepithelial carcinoma show loss of INI1 expression. However, epithelial and myogenic markers are generally negative in MPNSTs.  Proximal-type epithelioid sarcoma generally exhibit more uniform sheet-like architecture and rhabdoid cytomorphology without the typical trabecular or reticular areas found in most myoepithelial carcinomas. Moreover, the stromal component of myoepithelial tumors is absent in epitheloid sarcomas. Loss of INI1 expression, which is found in more than 90% of epithelioid sarcomas, is not useful in this context, given that a significant minority of myoepithelial carcinomas show loss of INI1 staining. 
In conclusion, we have described an extremely rare case of myoepithelial carcinoma arising in the rib which in addition to the usual diagnostic IHC markers also expressed ER and PR. This case further defines the immunohistochemical spectrum of myoepithelial tumors of soft tissue and expands it to include rare estrogen and progesterone receptor positivity.
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[Figure 1], [Figure 2]