Breast hamartoma is a rare benign tumor that comprises lobular breast tissues with various admixtures of fibrous, fibrocystic, and adipose tissue. Hamartoma accounts for 0.7%-5.0% of all benign breast tumors. Myoid hamartoma is an extremely rare variant of mammary hamartoma characterized by the presence of smooth muscle component. Herein, we report a case of myoid hamartoma showing irregular margins and microcalcifications with a literature review.
Hamartoma of the breast is a rare, genetically linked, benign tumor that is characterized by an abnormal growth of mammary tissues including ducts, lobules, stroma, and adipose tissue [
Myoid hamartoma, first described by Davies and Riddell in 1973, is an extremely rare subtype that is characterized by the presence of histologically normal, but irregular, randomly distributed, smooth muscle cells [
This study was approved by the Institutional Review Board at the Chonnam National University Hwasun Hospital (IRB No. CNUHH-2020-108).
A 44-year-old woman presented with a 2-year history of a mass in her left breast. The mass seemed to increase in size approximately six months before presenting to the hospital. Mammography of the left breast revealed an oval calcified mass that was partly indistinct (
Breast hamartoma tends to be under-recognized despite the advent of diagnostic procedures such as mammography, breast ultrasonography, and core needle biopsy [
Moreover, the pathogenesis of the myoid component in myoid hamartoma remains unclear. Various hypotheses have been proposed to explain the origin of smooth muscle stroma, and it is considered that it possibly originates from the myoepithelial cells, stromal myofibroblasts, vascular smooth muscle cells, or stromal stem cells [
Clinically, most myoid hamartomas are asymptomatic and are detected on mammography or breast ultrasonography [
The histological composition of myoid hamartoma varies depending on the relative proportion of glandular, adipose, fibrous, and myomatous elements [
Immunohistochemical studies are also helpful in establishing a diagnosis of myoid hamartoma, and several reports have suggested that spindle tumor cells show strong positive staining for smooth muscle actin, desmin, and vimentin, and the absence of staining for cytokeratin and S-100 protein [
The histological differential diagnoses of myoid hamartoma include various spindle cell tumors and tumor-like lesions showing specifically smooth muscle differentiation [
Local excision is the treatment of choice for myoid hamartoma. However, there are case reports showing coincidental cancer or local recurrence after surgery [
Here, we report a rare case of mammary myoid hamartoma showing irregular margins and microcalcifications.
The authors declare that they have no competing interests.
(A) Mammography reveals an oval calcified mass with partially indistinct margins. (B) Breast ultrasonography reveals a 1.7-cm irregular indistinct hypoechoic mass with calcifications.
Microscopical findings. (A) The mass comprises glandular structures, fibrous stroma, and mature adipose in various proportions (hematoxylin and eosin [HE stain], × 40). (B) The stroma reveals areas with high collagen concentration and elongated spindle cells without atypia (HE stain, × 400). (C) The spindle cells are intermixed with glandular elements (HE stain, × 400). (D) Scan view shows an irregular mass with microcalcifications (arrows) (HE stain, × 4).
Immunohistochemical findings. (A) Smooth muscle actin, (B) desmin, and (C) smooth muscle myosin heavy chain are strongly positive in spindle cells, while (D) S-100 protein is negative.