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J Clin Pathol. 2007 September; 60(9): 1057–1058.
PMCID: PMC1972433

Rare co‐existence of multifocal myoepitheliosis with infiltrating ductal carcinoma of the breast

Lesions composed of myoepithelial cells are known to occur in salivary gland, but they are uncommon in the breast.1 These range from benign lesions, such as myoepithelioma, to malignancies, such as adenoid cystic carcinoma and myoepithelial carcinoma. The predominance myoepithelial cells mainly in the terminal duct‐lobular units (TDLUs) with formation of multifocal lesions is termed myoepitheliosis.2 In the breast, this condition has been reported previously with other benign lesions such as sclerosing adenosis.

Recently, a role for myoepithelial cells in the pathogenesis of carcinoma has also been suggested. There are no previous reports describing the occurrence of myoepitheliosis with breast carcinoma. This report describes a unique case of dual occurrence of myoepitheliosis with infiltrating ductal carcinoma (IDC). We hope that future studies will disclose the relationship, if any, between the two lesions.

Case report

A 40‐year‐old woman presented to the surgical outpatient department with a lump in the left breast for the last 6 months. On examination, a hard mass was seen in the central part. A mammographic examination showed it to be a high‐density lesion with foci of microcalcification. Fine‐needle aspiration cytology from the mass showed the presence of an IDC. A left‐sided modified radical mastectomy with axillary clearance was performed subsequently, and the specimen was sent for histopathological examination.

Pathological findings

Grossly, the specimen comprised left breast with overlying elliptical skin flap bearing the nipple, areola and axillary tail. Serial slicing showed two nodules—the larger one located centrally, measuring 6×4×4 cm, and the smaller one located in the left upper quadrant, measuring 2×1×1 cm. The larger nodule was situated close to the deep resection plane (0.2 cm), but the skin, nipple and areola were free. Adequate sections were taken from both nodules for microscopy and all the axillary lymph nodes were sampled.

The larger nodule showed an IDC, grade II, on microscopy (Elston and Ellis modification of Bloom Richardson classification).3 The tumour extended close to the deep resection plane; however, it was free. The smaller nodule showed multiple foci of proliferating oval to spindle cells, involving almost all the TDLUs as well as the surrounding areas ((figsfigs 1 and 22).). Similar foci were also identified in the sections taken from peritumoural (fig 33)) and tumour‐free areas. The intervening stroma showed fibrosis. No atypia or mitosis was noted. The myoepithelial nature of these cells was confirmed by smooth muscle actin (SMA) and S‐100 immunostaining. There was no evidence of any malignant change in the epithelial component in this nodule. Considering the above features, a diagnosis of IDC with multifocal myoepitheliosis was made. The lymph nodes from the axillary tail were free of tumour.

figure cp42531.f1
Figure 1 A focus of myoepitheliosis showing proliferation of cuboidal to spindle‐shaped myoepithelial cells leading to the formation of a nodule.
figure cp42531.f2
Figure 2 Infiltrating ductal carcinoma (broad arrow) with a focus of myoepitheliosis in the adjoining breast (arrow).
figure cp42531.f3
Figure 3 High‐power photomicrograph showing the proliferating oval to spindle myoepithelial cells.

Discussion

Myoepithelial lesions of the breast range from the myoepithelial proliferations accompanying benign lesions—for example, sclerosing adenosis, ductal hyperplasia and nipple adenoma—to malignancies such as adenoid cystic carcinoma, adenomyoepithelioma and myoepithelial carcinoma. Myoepitheliosis is a benign condition characterised by multifocal proliferation of spindle to cuboidal myoepithelial cells generally located in the TDLUs. It can occur in two forms: the intraductal form, in which there is variable distention and occlusion of the TDLUs, and periductal form, which is often associated with sclerosis. The periductal variety, now considered a variant of sclerosing adenosis, may sometimes be misdiagnosed as an invasive carcinoma, particularly in the background of atrophy.2 The present case highlights a mixed pattern with both intraductal and periductal components. Myoepitheliosis generally does not present as a mass lesion. However, if myoepithelial cells form aggregates, it may sometimes be felt as a nodule, as was seen in our case.2 Immunohistochemically, the cells exhibit positivity for protein markers such as SMA and S‐100 protein.4 The recently described nuclear protein p63 is also considered to be sensitive and specific for identification of myoepithelial cells.5 Our case showed positivity for SMA as well as S‐100 protein, but the intensity of staining was stronger for SMA. Tavassoli2 described three patients with myoepitheliosis in a series of myoepithelial lesions of the breast. None of her patients, however, had a coexisting IDC.

The exact contribution of myoepithelial cell proliferation to ductal carcinomas is unclear. Several reports suggest that 2–18% of the IDC show focal or diffuse myoepithelial differentiation by immunohistochemical protein markers (eg, basal cytokeratins, actin, calponin, caldesmon and S‐100 protein). Experimental studies have shown a considerable overlap between the genetics of lesions arising from myoepithelial and epithelial cells, and it has been suggested that the two cell types are derived from the same precursor.6 Also, the myoepithelial cells have been shown to secrete a variety of tumour‐suppressor molecules, such as maspin, laminin‐1 and Wilms' tumour‐1, which are thought to have anti‐invasive and antiangiogenic effects on carcinoma and precancer cells. The loss of these molecules due to myoepithelial cell injury may lead to cell proliferation, angiogenesis and invasion.7,8 Excision is the treatment of choice in myoepitheliosis. However, in the present case, the future course of treatment and outcome depend on the coexistent malignancy.2

To conclude, we document the presence of a rare multifocal myoepitheliosis in a case of IDC. However, the link between the two lesions in the same breast cannot be explained from this single case report. Future studies are needed to establish the exact role of such proliferations of myoepithelial cells in breast malignancies.

Footnotes

Competing interests: None declared.

References

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8. Gudjonsson T, Ronnov‐Jessen L, Villadsen R. et al Normal and tumor‐derived myoepithelial cells differ in their ability to interact with luminal breast epithelial cells for polarity and basement membrane deposition. J Cell Sci 2002. 11539–50.50 [PubMed]

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