Definition/General
Introduction:
Usual ductal hyperplasia (UDH) is a benign proliferative breast lesion characterized by an increased number of epithelial cells within a duct, without cytological atypia
It is also known as epitheliosis.
Origin:
UDH arises from the terminal duct-lobular unit (TDLU)
It is a polyclonal proliferation of epithelial, myoepithelial, and metaplastic apocrine cells.
Classification:
UDH is classified as a benign proliferative breast lesion without atypia
It is distinguished from atypical ductal hyperplasia (ADH) by its cytological and architectural features.
Epidemiology:
UDH is an extremely common finding in breast biopsies and is often associated with fibrocystic changes
It can be seen in women of all ages but is most common in the perimenopausal period.
Clinical Features
Presentation:
UDH is typically an incidental microscopic finding and is not associated with a palpable mass
It can be associated with mammographic calcifications.
Symptoms:
Asymptomatic.
Risk Factors:
Not applicable.
Screening:
UDH can be associated with microcalcifications on mammography.
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Gross Description
Appearance:
There are no specific gross findings for UDH.
Characteristics:
Not applicable.
Size Location:
Not applicable.
Multifocality:
UDH is often multifocal.
Microscopic Description
Histological Features:
The ducts are filled with a proliferation of epithelial cells in a haphazard arrangement
The cells are heterogeneous, with variable sizes and shapes
The key features are irregular, slit-like secondary lumens at the periphery of the duct and cellular streaming and swirling.
Cellular Characteristics:
The cells are a mixed population of epithelial and myoepithelial cells
The nuclei are oval to spindle-shaped, with fine chromatin and inconspicuous nucleoli
There is nuclear overlapping and variation in cell orientation.
Architectural Patterns:
The proliferation is solid or fenestrated, with irregular, slit-like spaces
Cellular streaming, swirling, and bridging are characteristic.
Grading Criteria:
This is a benign lesion.
Immunohistochemistry
Positive Markers:
UDH shows a mosaic or mixed pattern of staining for cytokeratins
It is positive for both low molecular weight (e.g., CK7, CK8/18) and high molecular weight (e.g., CK5/6) cytokeratins
It is also positive for ER, but the staining is typically weak and heterogeneous.
Negative Markers:
Not applicable.
Diagnostic Utility:
IHC for CK5/6 is very useful to differentiate UDH (mosaic positivity) from ADH and low-grade DCIS (negative).
Molecular Subtypes:
Not applicable.
Molecular/Genetic
Genetic Mutations:
UDH is a polyclonal proliferation and does not typically show the clonal genetic alterations seen in ADH and DCIS.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
UDH is associated with a small increased risk (about 1.5-2 fold) of developing invasive breast cancer.
Therapeutic Targets:
No specific treatment is required for UDH
Management is focused on the associated lesions, if any.
Differential Diagnosis
Similar Entities:
Atypical ductal hyperplasia (ADH)
Low-grade DCIS.
Distinguishing Features:
ADH and low-grade DCIS are composed of a monotonous population of cells, form rigid, geometric spaces, and are negative for CK5/6
UDH has a heterogeneous cell population, irregular slit-like spaces, and a mosaic pattern of CK5/6 staining.
Diagnostic Challenges:
The main challenge is distinguishing florid UDH from ADH or low-grade DCIS
The architectural pattern and IHC for CK5/6 are key distinguishing features.
Rare Variants:
Not applicable.
Sample Pathology Report
Template Format
Sample Pathology Report
Complete Report: This is an example of how the final pathology report should be structured for this condition.
Specimen Information
[specimen type], measuring [size] cm in greatest dimension
Diagnosis
[diagnosis name]
Classification
Classification: [classification system] [grade/type]
Histological Features
Shows [architectural pattern] with [nuclear features] and [mitotic activity]
Size and Extent
Size: [X] cm, extent: [local/regional/metastatic]
Margins
Margins are [involved/uninvolved] with closest margin [X] mm
Lymphovascular Invasion
Lymphovascular invasion: [present/absent]
Lymph Node Status
Lymph nodes: [X] positive out of [X] examined
Special Studies
IHC: [marker]: [result]
Molecular: [test]: [result]
[other study]: [result]
Final Diagnosis
Final diagnosis: [complete diagnosis]