Leiomyoma of the breast parenchyma: a case report and review of the literature

ABSTRACT INTRODUCTION: Benign tumors are often seen in breast screening examinations. However, the differential diagnosis is not always simple because of radiological similarity between the different benign lesions. CASE REPORT: We present a rare case report of leiomyoma of the breast parenchyma in a 68-year-old asymptomatic patient. The mammographic and ultrasonographic findings were similar to those observed in benign lesions. CONCLUSION: The histopathological diagnosis requires careful differentiation from lesions that have smooth muscle proliferation, especially leiomyosarcoma. The most commonly performed treatment is resection of the lesion with free margins. Although breast leiomyoma is rare, it should be considered among the differential diagnoses for breast nodules of benign appearance. Resection with safety margins proved to be the only treatment needed.


INTRODUCTION
Leiomyoma is considered to be the rarest non-epithelial tumor of the breast. 1 It occurs more frequently in the retroareolar region because of the greater amount of smooth muscle in this location. 2 Its presence in the mammary parenchyma is extremely rare, with fewer than 30 cases reported so far in the literature. 3 The clinical, radiological and pathological characteristics do not differ markedly from those observed in the most frequent benign lesions. We report a case of leiomyoma in the breast parenchyma that was seen in our service and conducted a review of the literature, with special attention to radiological features that have been described so far.

CASE REPORT
A 68-year-old woman was seen at the Division of Mastology, Department of Gynecology of the Federal University of São Paulo (Universidade Federal de São Paulo, UNIFESP) with a non-palpable tumor that had been detected through screening mammography. The patient presented controlled hypertension and minor degenerative osteoarticular alterations. She reported having had three pregnancies and two deliveries, with thirty months of breastfeeding. She said that she did not have any other symptoms such as papillary flow or cutaneous lesions. She reported having had routine annual mammograms and that she had not had any previous surgery or biopsies. The mammogram performed two years earlier did not show any abnormalities. The physical examination was unremarkable, with no evidence of any palpable mass, skin changes or axillary lymphadenopathy.

Imaging findings
Mammographic images showed an isodense circumscribed oval mass measuring 1.8 x 1.0 cm that was located at the junction of the upper quadrants of the left breast. Sonographic images of the left breast showed a hypoechoic homogenous oval mass measuring 1.4 x 0.7 cm that was horizontal and parallel to the skin. It had two lobulations and circumscribed margins, and was coincident with the location described through mammography (Figure 1). The lesion did not present any posterior acoustic shadow, hyperechoic halo or other associated abnormal features. The mass was classified as being in Breast Imaging-Reporting and Data System (BI-RADS) category 4.

Histopathological findings
An ultrasound-guided breast core biopsy with a 12-gauge needle was performed and five fragments were obtained. The necrosis or mitotic figures was found. Immunohistochemical stains for CD34 and S100 were positive, and negative for desmin and smooth muscle actin. A diagnosis of smooth muscle tumor, and specifically mammary parenchyma leiomyoma, was established. There was no recurrence of the lesion after followup of 60 months.

DISCUSSION
Even though Strong's first paper on breast leiomyoma was published in 1913, knowledge of the etiology of this condition remains uncertain. 4 It has been taken to originate from smoothmuscle angiomatous cells, given the "angiocentric" proliferation of smooth muscle that is observed. This theory is reinforced through the observation that blood vessels are present at locations showing defects or artefacts of histological fixation. 5 Current immunohistochemical findings rule out teratogenic origins. Uncertainty remains regarding theories of embryological displacement of smooth muscle cells of the areola, and regarding an origin from multipotent mesenchymal cells. These were proposed in the first half of the twentieth century by Melnick 6 and Shauder. 7 Breast leiomyoma occurs predominantly in women, with only one case reported in a man. 2 The age of highest incidence is between 40 and 60 years. It presents as an isolated tumor of slow growth, with similar characteristics to the most common benign tumors. [8][9][10] The presence of pain was observed in only three cases, being more frequent in tumors of areolar location due to the contraction of neoplastic muscle cells. 11 Physical examination usually reveals a mobile nodule with welldefined limits and fibroelastic consistency, although sometimes it has been reported to have hardened consistency. [12][13][14] Mammographic images have been described as showing an isodense or hyperdense oval mass, with outlines that are most often circumscribed (Table 1). 1,13,[15][16][17][18][19][20][21] Microcalcifications relating to leiomyoma have never been described. 15,16,22,23 The effectiveness of mammography is limited in relation to lesions measuring less than 1.0 cm and breasts with predominant glands. Sonography frequently shows a hypoechoic mass with well-defined limits and oval shape. 17 Presence of lobulations has frequently been observed. Growth parallel to the skin has been observed in 100% of the cases. No well-defined posterior acoustic shadowing has been described. 18 Magnetic resonance imaging findings were first reported

MMG = mammogram. US = ultrasonography
In cases of lesions suggestive of leiomyoma, leiomyosarcoma is the main situation that needs to be ruled out. 19,27 Presence of 2-16 mitotic figures per 10 high-power figures is the main feature for diagnosing leiomyosarcoma. According to Pourbagher, presence of 1-3 mitotic figures might be considered to represent an intermediate category because of the higher risk of local recurrence and, therefore, treatment that is more radical. 15 Boscaino et al. reported local recurrence in two cases initially diagnosed as leiomyoma. Histological reevaluation of the lesions found presence of increased mitotic activity, and the lesions were reclassified as smooth-muscle neoplasms of undetermined prognosis. 28 In patients with a confirmed diagnosis of breast leiomyoma, no cases of local recurrence have been reported to date. [11][12][13][14][15][16][17][18][19][22][23][24][25][26][27] We reviewed the literature in MEDLINE and Lilacs using the English keywords "leiomyoma", "fibroid tumors", "benign tumor", "benign neoplasms", "breast tumor", "breast neoplasms" and "ultrasonography". We found 30 case reports that described patients with leiomyoma in the breast parenchyma ( Table 2).

CONCLUSION
In conclusion, it can be said that leiomyoma in mammary tissue is an extremely rare condition. The clinical presentation does not differ from that observed in the most common benign tumors of the breast. The radiological findings are characteristically benign, which helps rule out the hypothesis of cancer. In histopathological evaluations, it is important to pay attention to the differential diagnosis of leiomyosarcoma. The standard recommended treatment is local resection with free margins. In this situation, the risk of local recurrence is practically zero.