Terminal ductal lobular unit

Last revised by Dr Mostafa El-Feky on 09 Mar 2021

Each breast lobe is drained by a collecting duct terminating in the nipple. The collecting duct has several branches, which ends in a terminal ductal-lobular unit (TDLU), the basic functional and histopathological unit of the breast. The TDLU is composed of a small segment of the terminal duct and a cluster of ductules, which are the effective secretory units. The functional structures are surrounded by specialized connective tissue. A normal terminal ductal-lobular unit ranges from 1-4 mm.

The TDLU consists of the:

  • extralobular terminal duct 
  • intralobular terminal duct 
  • lobule (functional unit of the breast)


This is the most important structure in the breast. It is the glandular unit that produces milk.

Related pathology

It is postulated that most cancers and benign lesions arise in the terminal duct either inside or just proximal to the lobule. For example:

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Cases and figures

  • Case 1
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  • Case 2
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