Epithelioid cells in myoid hamartoma of the breast: a potential diagnostic pitfall for core biopsies.

OBJECTIVE

We report six cases of myoid hamartoma of the breast, a rare benign lesion in which the characteristic smooth muscle cells may have epithelioid histology. We emphasize the importance of radiographic correlation and immunohistochemical studies to diagnosis, particularly on stereotactic core biopsies, to avoid potential confusion with infiltrating lobular carcinoma.

DESIGN

Case studies. Prospective and retrospective analysis of six cases, including stereotactic biopsy of two.

SETTING

Academic medical center-based pathology practice.

PATIENTS

Six postmenopausal women, aged 50 to 59 years, with palpable or nonpalpable mammographically evident breast masses.

RESULTS

All the lesions were radiographically well circumscribed, most showing heterogeneous radiodensity. Histologically variable amounts of glandular, fibrous, and adipose tissue were admixed with smooth muscle cells, which occasionally had prominent epithelioid features. All the lesions' myoid cells stained for smooth muscle markers as well as steroid receptor proteins. Stereotactic core biopsy was diagnostic in one case, making excision unnecessary.

CONCLUSIONS

With proper radiographic correlation and immunohistochemical confirmation, myoid hamartoma can be confidently diagnosed even on the limited tissue samples yielded by stereotactic core biopsy.