Myoid Hamartoma of the Breast With HMGA2 Rearrangement and Associated In-Situ and Invasive Carcinoma: Case Report and Review of Literature.

Myoid hamartoma of the breast is an uncommon benign breast neoplasm. We describe an unusual example of an in-situ and invasive carcinoma arising in a myoid hamartoma. We also describe the unique molecular findings in the myoid hamartoma and review the pertinent literature. In radiology studies, the mammogram showed increased density/attenuation, and the ultrasound revealed a change in the overall echogenicity with hyperechoic and anechoic areas. The stromal compartment contained smooth muscle bundles and adipose tissue on microscopic examination. The stromal cells showed HMGA2 gene rearrangement by fluorescence in-situ hybridization analysis and overexpression of HMGA2 by immunohistochemistry. The breast myoid hamartoma is likely underpinned by HMGA2 gene rearrangement and HMGA2 protein overexpression, which can be used as an ancillary test to diagnose this rare breast lesion. Although most myoid hamartomas have a benign clinical course, the likelihood of malignant transformation should always be considered.