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CASE REPORT
CytoJournal 2007,  4:3

Cytologic findings in malignant myoepithelioma: a case report and review of the literature


Department of Pathology, Faculty Division Ullevaal University Hospital, N-0407 Oslo, Norway

Date of Submission11-Sep-2006
Date of Acceptance25-Jan-2007
Date of Web Publication25-Jan-2007

Correspondence Address:
Torill Sauer
Department of Pathology, Faculty Division Ullevaal University Hospital, N-0407 Oslo
Norway
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Source of Support: None, Conflict of Interest: None


DOI: 10.1186/1742-6413-4-3

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 » Abstract 

Background: Myoepithelioma of the breast is a rare tumor and the cytologic features have only been described in one previous report.
Case presentation: The present case comprises a 70 year old woman with a mammographic equivocal and ultrasonographic suspicious lesion. The aspirates were cellular and consisted mainly of single spindle or polymorphic, polygonal cells. The nuclei were generally large, ranging from 2 - > 5 × RBC. Most nuclei had a distinct medium-sized nucleolus. The nuclear outlines were irregular with buds and folds. The chromatin was granular. In the background there was abundant granular metachromatic ground substance and some metachromatic stromal fragments. A few mitotic figures were found. The cytologic diagnosis was suspicious for malignancy and a metaplastic carcinoma where only the non-epithelial component had been aspirated, or a non-epithelial lesion, was suggested.
Macroscopically the tumor was round, seemingly well circumscribed, firm and with a white cut surface. The lesion consisted of spindled and polygonal cells with distinct pleomorphism. There were 6-9 mitoses per high power field (HPF). The tumor infiltrated in the surrounding fatty tissue. On immunohistochemistry, tumor cells were positive for smooth muscle actin, keratin MNF 116 and vimentin. Desmin and S-100 were negative.
Ultrastructurally, there were abundant tonofilaments, including globular filamentous bodies and granulated endocytoplasmic reticulum with many dilated cisterns. The histologic diagnosis was malignant myoepithelioma.
Conclusion: The case mirrors completely the WHO definition and the previous cytological and histological descriptions of malignant myoepitheliomas in the literature which describe a spindle cell population with unequivocal nuclear atypia, metachromatic background substance and mitoses.



How to cite this article:
Sauer T. Cytologic findings in malignant myoepithelioma: a case report and review of the literature. CytoJournal 2007;4:3

How to cite this URL:
Sauer T. Cytologic findings in malignant myoepithelioma: a case report and review of the literature. CytoJournal [serial online] 2007 [cited 2017 Aug 24];4:3. Available from: http://www.cytojournal.com/text.asp?2007/4/1/3/41220



 » Background Top


Myoepithelioma of the breast is a rare tumor. It usually presents as a palpable nodule, and a mammographic density without distinctive features. Most are benign, and only few malignant cases have been reported in the literature [1-4]. The patient age may range from 22 to 87 years. WHO Classification of Tumours: "Tumours of the Breast and Female genital Organs" [5] define malignant myoepithelioma as an infiltrating tumour composed purely of myoepithelial cells (predominantly spindled) with identifiable mitotic activity. They may vary in size from 1 cm to 21 cm. The cytologic findings in a malignant myoepithelioma have been described in one previous report [6]. This paper describes the findings in an additional case. The findings are compared with the characteristic features of histologic findings that are described in the literature.


 » Case presentation Top


Clinical history

A 70-year old woman attended mammography screening. The mammograms revealed en equivocal lesion. Ultrasonography identified a 14 mm tumor that was suspicious for malignancy. A FNAC was done under ultrasound guidance.

FNAC findings

The smears were stained with Diff-Quick® (Dade AG, Düdingen, Germany). The aspirates were cellular and consisted mainly of single spindle or polymorphic, polygonal cells with a few admixed groups of benign ductal epithelial cells [Figure 1] and lymphocytes.

The nuclei were generally large, ranging from 2 - > 5 × RBC. Most nuclei had a distinct medium-sized nucleolus. The nuclear outlines were irregular with buds and folds. The chromatin was granular. A few cells showing intranuclear cytoplasmic vacuoles were found [Figure 2]. The cytoplasm was bluish, variable in amount and often dense [Figure 3]. In the background there was abundant granular metachromatic ground substance and some metachromatic stromal fragments [Figure 2], [Figure 4] and [Figure 5].A few mitotic figures were found [Figure 6]. There was no necrotic debris.

The cytologic diagnosis was suspicious for malignancy and a metaplastic carcinoma where only the non-epithelial component had been aspirated, or a non-epithelial lesion, was suggested. No smears were available for immunocytochemistry.

Histopathological findings

The histopathological characteristics are shown in [Figure 7],[Figure 8],[Figure 9],[Figure 10],[Figure 11],[Figure 12],[Figure 13],[Figure 14],[Figure 15],[Figure 16],[Figure 17],[Figure 18]Macroscopically the tumor was round, seemingly well circumscribed, firm and with a white cut surface. The diameter was 14 mm. On microscopy, the lesion was cellular [Figure 7] and [Figure 8], consisting of spindled and polygonal cells with distinct pleomorphism [Figure 9],[Figure 10],[Figure 11].There were variable amounts of eosinophilic ground substance [Figure 8],[Figure 12] and [Figure 13] and a focal admixture of lymphocytes [Figure 9] and [Figure 14].There were 6-9 mitoses per high power field (HPF) [Figure 15] The tumor infiltrated in the surrounding fatty tissue [Figure 16],[Figure 17],[Figure 18].

On immunohistochemistry, the tumor cells were positive for smooth muscle actin (DAKO, Glostrup, Denmark) [Figure 19], keratin MNF 116 (a pan-keratin with both high- and low molecular weight keratins from DAKO, Glostrup, Denmark) [Figure 20] and vimentin (DAKO, Glostrup, Denmark) [Figure 21] .About 30 % of the tumor cell nuclei were positive for Ki-67 (DAKO, Glostrup, Denmark) [Figure 22]. Desmin (DAKO, Glostrup, Denmark) and S-100 (DAKO, Glostrup, Denmark) were negative. Estrogen- and progesterone receptors (DAKO, Glostrup, Denmark) as well as HER-2 (Novocastra, Newcastle upon Tyne, UK) were all negative.

Ultrastructurally, there were abundant tonofilaments [Figure 23],including globular filamentous bodies and granulated endocytoplasmic reticulum with many dilated cisterna. Desmosomes were not identified, but the tissue was poorly preserved. A few lysosomes were seen.

The histologic diagnosis was malignant myoepithelioma. The sentinel axillary lymph node was examined and was negative.


 » Discussion Top


The cytologic features in this case presented solely with mesenchymal appearing cells with a distinct nuclear atypia. This is in keeping with previous histologic reports that malignant myoepitheliomas usually present with a spindle cell population and no epithelial cell component [1, 2, 4]. Kurashini et al [6] reported a case of malignant myoepithelioma consisting mainly of spindle-shaped cells with a few admixed epithelial cells. They reported nuclear atypia with hyperchromasia and prominent nucleoli, occasional intranuclear cytoplasmic inclusions and mitoses. Our findings are practically identical. Kurashina et al did not comment upon the ground-/background substance, which probably was difficult to appreciate in their Papanicolaou stained smears where it is well known that extracellular material might be difficult or impossible to see.

The cytological criteria of benign myoepitheliomas of the breast are known [7-12]. They present with a dual cell population with clusters of both epithelial and spindled cells. The cells may show a mild to moderate nuclear pleomorphism, occasional intranuclear cytoplasmic vacuoles, naked bipolar cells and a metachromatic, fibrillary, myxoid material, but no necrosis or mitoses.

The cytological criteria of malignant myoepitheliomas have not been established, but the findings are concurrent in the case of Kurashini et al [6] and our case. Both cases mirror completely the WHO definition [5] and the histological descriptions of malignant myoepitheliomas in the literature [1-4] which describe a spindle cell population with unequivocal nuclear atypia, metachromatic background substance and mitoses.

The cytologic differential diagnoses of malignant spindle cell tumors include borderline and malignant phyllodes tumor, soft tissue sarcomas as leiomyosarcoma, fibrosarcoma, malignant fibrous histiocytoma and malignant schwannoma. Immunocytochemical stains may be of help when additional smears, cell suspensions or cell blocks are available. A suitable panel of markers would include antibodies against epithelial and myoepithelial differentiation, mesenchymal and smooth muscle as well as neural differentiation. Positivity for epithelial and myoepithelial markers would rule out phyllodes tumor and all types of soft tissue sarcomas.

Another important differential diagnosis is metaplastic carcinoma. In most cases of FNAC from metaplastic carcinomas there will be a distinct carcinomatous component. A few cases may present only the mesenchymal appearing component on FNAC. In contrast to malignant myoepithelioma, the mesenchymal component in metaplastic carcinomas will express epithelial markers, at least focally with the exception of rare true carcinosarcomas. The combined epithelial/myoepithelial immunophenotype may be found in some metaplastic carcinomas also. A preoperative, cytologic and immunocytologically distinction between a malignant myoepithelioma and a metaplastic carcinoma where only the mesenchymal appearing component is present might not always be possible.


 » Conclusion Top


This case mirrors completely the WHO definition and the previous cytological and histological descriptions of malignant myoepitheliomas in the literature which describe a spindle cell population with unequivocal nuclear atypia, metachromatic background substance and mitoses. Immunocytochemistry might aid in narrowing the differential diagnoses, but a specific cytologic diagnosis might still not be possible.


 » Abbreviations Top


HPF = high power field

RBC = red blood cell

WHO = world health organization

FNAC = fine needle aspiration cytology


 » Conflicts of interest Top


There are no conflicts of interest

This case report is the sole work of the author Torill Sauer.


 » Acknowledgements Top


The ultrastructural image was kindly provided by Dr. Magnus Rψger, Department of Pathology, Ullevaal University Hospital.

 
 » References Top

1.Jennens RR, Rosenthal MA, Gonzales M: Metastatic myoepithelioma of the breast. ANZ 2004, 74: 1135-1137.  Back to cited text no. 1    
2.Shiraishi T, Nakayama T, Fukutome K, Watanabe M, Murata T: Malignant myoepithelioma of the breast metastasizing to the jaw. Virchows Arch 1999, 435: 520-523.  Back to cited text no. 2    
3.Sugano I, Nagao T, Tajima Y, Ishida Y, Nagao K, Ooeda Y, Takahashi T: Malignant adenomyoepithelioma of the breast: a non-tubular and matrix-producing variant. Pathol International 2001, 51: 193-199.  Back to cited text no. 3    
4.Thorner PS, Kahn HJ, Baumal R, Lee K, Moffatt W: Malignant myoepithelioma of the breast. An immunohistochemical study by light and electron microscopy. Cancer 1986, 57: 745-750.  Back to cited text no. 4    
5.Tavassoli FA, Soares J: Myoepithelial lesions in the breast. WHO Classification Tumour Pathology & Genetics. Tumours of the Breast and female Genital Organs 2004, 86-88. [ WHO Classification Tumour Pathology & Genetics. ]   Back to cited text no. 5    
6.Kurashina M: Fine-needle aspiration cytology of benign and malignant adenomyoepithelioma: report of two cases. Diagn Cytopathol 2002, 26: 29-34.   Back to cited text no. 6    
7.Chang A, Bassett L, Bose S: Adenomyoepithelioma of the breast: a cytologic dilemma. report of a case and review of the literature. Diagn Cytopathol 2002, 26: 191-196.   Back to cited text no. 7    
8.Iyengar P, Ali SZ, Brogi E: Fine-needle aspiration cytology of mammary adenomyoepithelioma: a study of 12 patients. Cancer 2006, 108: 250-256.   Back to cited text no. 8    
9.McCluggage WG, McManus DI, Caughley LM: Fine needle aspiration /FNA) cytology of adenoid cystic carcinoma and adenomyoepithelioma of the breast: two lesions rich in myoepithelial cells. Cytopathology 1997, 8: 31-39.  Back to cited text no. 9    
10.Ng WK: Adenomyoepithlioma of the breast. A review of three cases with reappraisal of the fine needle aspiration biopsy findings. Acta Cytol 2002, 46: 317-324.  Back to cited text no. 10    
11.Ng WK: Fine-needle aspiration cytology of benign and malignant adenomyoepithlioma: report of two cases. Diagn Cytopathol 2002, 26: 29-34.   Back to cited text no. 11    
12.Pogacnik A, Golouh R, Flezar M: Adenomyoepithelioma of the breast diagnosed by fine needle aspiration (FNA) biopsy; a case report. Cytopathology 1997, 8: 45-52.  Back to cited text no. 12    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10], [Figure 11], [Figure 12], [Figure 13], [Figure 14], [Figure 15], [Figure 16], [Figure 17], [Figure 18], [Figure 19], [Figure 20], [Figure 21], [Figure 22], [Figure 23]

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