The field measures approximately 1.0 x 1.5 cm. L1 measures about 1 mm in diameter. 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.