Terminal duct lobular unit

Last revised by Raymond Chieng on 16 Jun 2023

Each lobe of the breast is drained by a collecting duct terminating in the nipple. The collecting duct drains several side branches, each arising from a terminal duct lobular unit (TDLU), the basic functional and histopathological unit of the breast. The terminal duct lobular unit 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.

Terminal duct lobular units consist of 8:

  • extralobular terminal duct

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

  • ductules - part of lobule


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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