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The Korean Journal of Pathology 2010; 44: 431-4DOI: 10.4132/KoreanJPathol.2010.44.4.431

Smooth muscle cell metaplasia is an extremely rare form of stromal differentiation in fibroade-nomas. We describe a case of fibroadenoma with exuberant smooth muscle cells in a 72-year-old woman. The mass was located in the upper central portion of the left breast. It waswell circumscribed and its greatest dimension was 3 cm. Histologically, the glandular elementsresembled the appearance of fibroadenoma, but the stromal elements were composed ofspindle cell bundles with abundant eosinophilic cytoplasm and elongated cigar-shaped nuclei.Neither mitotic activity nor cellular atypia was seen. The stromal cells were immunohistochem-ically positive for smooth muscle actin, calponin, desmin, and estrogen receptor-b, but negativefor CD34, S-100 protein, p63, CD10, estrogen receptor-a, progesterone receptor and cytok-eratin. These results proved that the stromal cells showed features of smooth muscle cells.

Key Words : Breast; Fibroadenoma; Muscle cells; Metaplasia

Ga-Eon Kim∙∙Young KimEun-Hui Jeong∙∙Jo-Heon KimMin-Ho Park1∙∙Ji Shin Lee

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Exuberant Smooth Muscle Cells in Fibroadenoma of the Breast

- A Case Report -

431 431

Corresponding AuthorJi Shin Lee, M.D.Department of Pathology, Chonnam National University Hwasun Hospital, 160 Ilsim-ri, Hwasun-eup,Hwasun 519-763, KoreaTel: 82-61-379-7072Fax: 82-61-379-7099E-mail: jshinlee@hanmail.net

Departments of Pathology and1Surgery, Chonnam National UniversityMedical School, Gwangju, Korea

Received : June 2, 2009Accepted : August 19, 2009

Fibroadenoma is the most common benign tumor of thebreast. It is comprised of epithelial and stromal components.Unusual smooth muscle cell differentiation - metaplasia - isencountered in a minority of fibroadenomas. Goodman andTaxy1 first reported two cases of fibroadenoma with prominentsmooth muscle cells. Fibroadenoma with smooth muscle cellsmust be distinguished from muscular hamartoma and leiomy-oma.1,2 Here we report a case of the fibroadenoma with exuber-ant smooth muscle cells, and review the relevant literature. Tothe best our knowledge, this is the first Korean report.

CASE REPORT

A 72-year-old woman presented with a palpable mass in theleft breast. She had first noticed the mass several years ago andsince then it remained unchanged. Physical examination reveal-ed a 3 cm mobile, well circumscribed, non-tender mass on thecentral upper area of the left breast. Breast ultrasonography con-firmed the presence of a 2.4 × 1.2 cm-sized, well-defined solid

mass with calcifications (Fig. 1). The patient underwent mam-motome biopsy of the mass under local anesthesia. Microscopi-cally, the tumor was well defined from normal breast tissues(Fig. 2A). The tumor contained glandular and stromal elements.The ducts were distorted into elongated and compressed slit-like structures, resulting in the so-called lumens of intracanalic-ular pattern (Fig. 2B). The epithelial cells in ducts did not revealhyperplasia. Stromal elements were mostly consisted of spindlecells with eosinophilic cytoplasm and elongated cigar-shapednuclei aggregated in small fascicles (Fig. 2C). Nuclear pleomor-phism and mitoses were absent. Some cores revealed adipocytesand dystrophic calcifications. Immunohistochemically, stromalspindle cells were strongly smooth muscle actin (1 : 200, Dako,Glostrup, Denmark), calponin (1 : 100, Dako), desmin (1 : 100,Dako), and estrogen receptor-b (ER-b; 1 : 20, Dako) positive,but did not express CD34 (1 : 300, Dako), S-100 protein (1 :1,000, Zymed Laboratories, South San Francisco, CA, USA),p63 (1 : 100, Dako), CD10 (1 : 100, Novocastra, Newcastle,UK), ER-a (1 : 75, Dako), progesterone receptor (1 : 200, Dako),and cytokeratin (1 : 100, Zymed Laboratories) (Fig. 3). The epi-

432 Ga-Eon Kim∙Young Kim∙Eun-Hui Jeong, et al.

thelial cells in ducts were only positive for ER-b. These micro-scopical and immunohistochemical findings proved that thespindle cells in stroma were smooth muscle cells. A final diag-nosis of fibroadenoma with exuberant smooth muscle cells wasestablished.

DISCUSSION

Smooth muscle cells have been considered as rare stromalcomponents of fibroadenoma since Goodman and Taxi1 first

reported two cases of fibroadenoma with prominent smoothmuscle. Of 85 cases of fibroadenoma, Shimizu et al.3 found 4(4.7%) that showed smooth muscle cells in the stroma. Thedistribution of smooth muscle cells was not diffuse. Three caseswere classified as intracanalicular subtype. In our case, the over-all histologic patterns were that of fibroadenoma with intra-canalicular pattern. The stromal component was predominant-ly comprised of spindle-shaped cells showing morphologicaland immunohistochemical features of smooth muscle cells.

The origin of the smooth muscle component in fibroadeno-mas is unknown. Apart from the elector muscle of the nipple,smooth muscle cells are usually absent in normal mammarystroma.4 Therefore, smooth muscle cells in fibroadenomas havebeen interpreted as a metaplastic process originating from stro-mal fibroblasts, myofibroblasts and myoepithelial cells.4 Shimizuet al.3 elucidated smooth muscle cells in the stroma, which hadmarked hyalinization and calcification. Therefore, they suggestedthat smooth muscle cells could appear in the stroma of long-standing tumors as a metaplastic process. Sapino et al.5 demon-strated that in cellular fibroadenomas, ER-b expression went inparallel with a smooth muscle differentiation phenotype of stro-mal cells, with these cells being positive for smooth muscle actinand/or calponin. They suggested a role of ER-b in myofibrob-lastic differentiation of stromal cells in fibroadenoma. In ourcase, the stromal elements did not express myoepithelial mark-ers, whereas expressed diffuse positivity for desmin, calponin,and ER-b. The stroma component had dystrophic calcification.The smooth muscle cells in our case may be derived from fibrob-lasts or myofibroblast and aging factors, and ER-b may partic-ipate in these transformations.

Fig. 1. Breast ultrasonography shows a 2.4 cm oval, well-circum-scribed mass with calcification (arrow).

Fig. 2. Microscopical findings. The tumor is well-defined from normal breast tissue (A). The ducts show elongated linear branching struc-tures with slit-like lumens (B). Stromal elements are predominantly comprised of spindle cells with eosinophilic cytoplasm and elongatedcigar-shaped nuclei (C).

A B C

Smooth Muscle Cells in Fibroadenoma of the Breast 433

The differential diagnoses of fibroadenomas with smooth mus-cle cells include leiomyoma and myoid hamartoma.2 Parenchy-mal leiomyoma is extremely rare. The diagnosis of leiomyomaof the breast should be restricted to lesions exclusively comprisedof smooth muscle cells.2,6 Myoid hamartoma is a very rare sub-type of breast hamartoma, characterized by the presence of smo-oth muscle cells. Unlike fibroadenoma, epithelial componentof myoid hamartoma shows normal mammary lobules.7 In our

case, the distinction from leiomyoma and myoid hamartomawas based on the presence of ductal-stromal proliferation, result-ing in an intracanalicular growth pattern.

In conclusion, we report a rare case of fibroadenoma with exu-berant smooth muscle cells, and conducted a review of the rele-vant literature. The smooth muscle component may be arisenfrom metaplastic changes of the mammary stroma.

Fig. 3. Immunohistochemically, spindle cells express a-smooth muscle actin (A), desmin (B), calponin (C), and estrogen receptor-b (D).Epithelial cells only express estrogen receptor-b.

A B

C D

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