RESUMO
Breast hamartoma is an uncommon poorly recognised benign breast neoplasm. Hamartoma displaying marked smooth muscle components known as myoid hamartoma of the breast is a much rarer entity. We present a case of myoid hamartoma of breast with chondroid differentiation in a 46-year-old woman. The painless breast lump was circumscribed and mammography showed a well-encapsulated large, dense mass with no calcification. Core needle biopsy was reported as fibroadenoma. The lesion was excised. Microscopically, it composed of many groups of mammary glandular components with dense fibrous stroma, adipose tissue and marked groups of smooth muscle fibres. Foci of chondroid differentiation were noted in the lesion. The smooth muscle cells showed strong and diffuse immunoreactivity for vimentin, myogloblin, alpha-smooth muscle actin, desmin and CD34 and failed to express pan-cytokeratin or S100 protein. The ducts lined by epithelial cells were reactive to pan-cytokeratin while the myoepithelial cells were reactive to S100 protein. The various immuno-histochemical staining as well as the cyto-histological changes encountered in myoid hamartomas are discussed with clinical, radiological and pathological correlation to differentiate it from other benign and malignant breast lesions.