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terminal duct lobular units

Tuesday 27 September 2016

TDLU; terminal duct lobular unit; TDLUs

Definition: The adult gland forms a tree-like structure starting at the nipple and branching through the stroma to end in lobules. The lobules are the ultimate milk producing functional units of the breast.

In the resting gland, the terminal lobules are referred to as the Terminal Ductal Lobular Unit (TDLU). TDLUs can be classified according to their complexity.

The terminal ductal lobular units (TDLUs) are the functional units of the breast. The TDLU consists of the extralobular terminal ducts and intralobular terminal ducts.

The intralobular terminal ducts form the central space of the lobule and have multiple outpouchings called acini or ductules.

The ductules differentiate into the secretory units during lactation. Intralobular stroma surrounds the lobules.

The milk is expulsed through the intra-lobular terminal ducts and the extra-lobular terminal ducts into the collecting ducts and through the lactiferous ducts to the nipple.

Pathology

Adenosis involves the epithelial and myoepithelial cells of the ductules.

Solitary (central) papillomas originate in the large ducts (segmental or subsegmental), but do not involve the TDLU. On the other hand multiple (peripheral) papillomas have a root in the TDLU and spread into the large ducts.

Cysts arise in the lobule, where the acini dilate, unfold, and then enlarge as fluid-filled cysts.

Modified Wellings Jensen model of breast cancer evolution

The model of ’ductal’ breast cancer evolution originally proposed by Wellings and Jensen was based almost entirely on the evidence of histologic continuity.

In this model, hyperplastic breast epithelial cells gradually enlarge normal TDLUs to form HELUs.

HELUs may then differentiate to microcysts (often with apocrine features) or progress to more complex lesions including UDH and ADH.

ADH may progress to DCIS as the cells continue to proliferate and distend the acini, and DCIS may eventually progress to IBC.

Progression is probably very slow overall and nonobligatory, so, for example, only a small subset of HELUs ever progress to ADH or beyond.

Whether and how differentiation and progression proceed is probably dictated by the acquisition of specific genetic and epigenetic abnormalities in a largely random manner.

ADH, atypical ductal hyperplasia; DCIS, ductal carcinoma in situ; HELU, hyperplastic enlarged lobular unit; IBC, invasive breast cancer; TDLU, terminal duct lobular unit; UDH, usual ductal hyperplasia.

References

Bassett LW et al. Breast Disease. Test and Syllabus. ACR (2000). p 14.
Ohuchi N, Abe R, Takahashi T, Tezuka F. Origin and extension of intraductal papillomas of the breast: a three-dimensional reconstruction study. Breast Cancer Res Treat. 1984;4(2):117-28.

Anomalies / Examples

columnar cell anomalies