10, 11, 12, 17, 18, 19, and 20. TDLU.

LEGEND

Slides 10, 11, 12, 17, 18, 19, 20. This is a portion of a slice of human mammary tissue. The field measures approximately 1.0 x 1.5 cm. Duct (D) and lobules(L1, L2, L3, L4) are indicated. L1 illustrates the primary anatomical and functional unit of the human breast; i.e., the "terminal ductal lobular unit" or TDLU. L1 measures about 1 mm in diameter. Note the individual terminal acini (or ductules) and the extralobular terminal duct (ETD). A careful distinction is made between "duct" and "ductule"; they are very different structures, not to be confused. Ductule and acinus are synonyms. The TDLU is the basic reacting unit in the human breast. All of the major lesions of the breast are believed to arise from the mammary epithelium of the TDLU, including fibroadenomas, apocrine cysts, various other cysts, sclerosing adenosis, microtubular adenosis, radial scars and preinvasive and invasive ductal and lobular carcinoma. Apparent exceptions are intraductal papilloma and papillary carcinoma. This histogenetic hypothesis is supported by strong circumstancial and statistical evidence. Hematoxylin stain.

10, 11, 12, 17, 18, 19, and 20. TDLU.

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