Myoepithilial tumours of the breast

Abstract

Myoepithelial lesions of the breast are defined as lesions arising from or composed of a dominant pure population of myoepithelial cells. They include adenoid cystic carcinoma, pleomorphic adenoma, myoepitheliosis, adenomyoepithelial adenosis, adenomyoepithelioma and myoepithelioma. The last two can be benign or malignant. Myoepithelial tumours of the breast are extremely rare. The benign myoepitheliomas are composed of a solid proliferation of cells with abundant eosinophilic syncytial cytoplasm. Although the biological behaviour of these remains uncertain, the tumours are considered to be myoepitheliomas with benign features due to mild nuclear pleomorphism, sparse mitotic figures and low ki67 index. Malignant myoepitheliomas represent the malignant end of the spectrum of myoepithelial lesions in the breast, usually arising de novo or in a pre-existing benign adenomyoepithelioma. Myoepitheliomas most often have spindle cell morphology and may mimic benign and malignant lesions. We report two cases of myoepithelial tumours and present a review of the current literature. Case presentation: The two patients were females aged 60 and 85 years, respectively. One patient had a palpable breast lump and the other presented as a firm mass without palpable axillary lymph nodes. The diagnosis of the first case was myoepithelioma with uncertain biological behaviour since the mitotic rate was 3-4mf/10High Power Field (HPF), and the second a malignant myoepithelioma due to the high mitotic rate. Conclusion: The patients were treated surgically and remain alive, two years after the initial diagnosis.