Anatomic Pathology: Breast Pathology

560) All of the following statements are true regarding the location of breast lesions EXCEPT:

• The image shows confluent sclerosing adenosis—note the lobulated growth pattern. Lesions of the breast typically are associated with specific locations in the breast, although the distribution is not always strict. Angiosarcoma may be primary in the breast or may manifest in skin usually after irradiation in the setting of conservative therapy (i.e., lumpectomy). Additionally, angiosarcoma may be seen away from the breast primarily in the skin of the upper extremity after lymph node dissection and lymphatic obstruction. In all of these instances, angiosarcoma may secondarily involve compartments from which it does not arise.

• The terminal duct lobular unit is the site of origin of changes typically characterized by cystic disease, including usual ductal hyperplasia, adenosis and sclerosing adenosis, atypical ductal or lobular hyperplasia, and lobular and ductal carcinoma in situ. Stem cells in this location are thought to give rise to both ductal and lobular tumors. The intralobular stroma is thought to be associated with the formation of fibroadenoma, and primarily periductal stroma is thought to be associated with phyllodes tumor. Peripheral papilloma, characterized by a mildly increased risk (1.5 to 2 relative risk) of development of invasive carcinoma, arises in the terminal duct lobular unit.

• The nipple and subareolar region are associated with numerous lesions, including Paget disease representing ductal carcinoma in situ arising in lactiferous ducts and extending into the epidermis. Also noted in the nipple is a potentially mass-forming lesion, florid papillomatosis of the nipple (also known as nipple adenoma); this lesion is characterized by ductular proliferation arising from lactiferous ducts and florid intraductal epithelial hyperplasia with varying degrees of atypia. Cancer may be associated with this lesion.

• Solitary intraductal papillomas, which are the most common cause of bloody nipple discharge, are seen in the subareolar region as well as in the nipple. Subareolar abscess formation may be seen in association with lactiferous ducts with squamous metaplasia. Terminal duct obstruction leads to duct rupture proximally with abscess formation. This condition typically requires abscess and duct excision.

• Duct ectasia is characteristically found in the subareolar location along with a sclerosing lesion referred to as subareolar sclerosing duct hyperplasia. The latter lesion is characterized by a geographic area of duct sclerosis and stromal elastosis with florid epithelial proliferation; this lesion is in the family of radial sclerosing lesions but tends to show less cyst formation. Subareolar sclerosing duct hyperplasia may be associated with carcinoma; however, the lesion itself is not a carcinoma, and careful attention should be paid to the geographic nature of the lesion and the presence of myoepithelial cells surrounding the intraductal epithelial proliferation, which may be highlighted with a smooth muscle actin, smooth muscle myosin heavy chain, or p63 immunostain. The smooth muscle actin immunostain should be interpreted carefully because sclerotic lesions may be strongly positive for smooth muscle actin.

• A rare lesion referred to as syringomatous adenoma of the nipple is a benign, locally infiltrating neoplasm histologically similar to the tumor of the skin. Syringomatous adenoma of the nipple does not appear to arise from skin, and it is not typically associated with intraductal epithelial proliferation. It should be distinguished from florid papillomatosis of the nipple (nipple adenoma). Syringomatous adenoma of the nipple comprises small tubular and ductular structures with elongated architecture in a teardrop shape. It has an infiltrative pattern that should not be confused with an invasive carcinoma, either well-differentiated or otherwise. The ducts are lined by one or more layers of small uniform cells.

Kumar V, Abbas AK, Fausto N, et al (eds): Robbins and Cotran Pathologic Basis of Disease, 8th ed. Philadelphia: Saunders, 2010.

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