Definition/General

Introduction:
-Epithelial hyperplasia of the breast, also known as usual ductal hyperplasia (UDH) or epitheliosis, is a benign proliferative lesion characterized by an increased number of epithelial cells within the ducts and lobules
-It is a very common finding.
Origin: It arises from the terminal duct-lobular unit (TDLU).
Classification: It is classified as a proliferative breast lesion without atypia.
Epidemiology: It is extremely common and is often an incidental finding in breast biopsies.

Clinical Features

Presentation: It is an incidental microscopic finding.
Symptoms: Asymptomatic.
Risk Factors: There are no well-established risk factors.
Screening: It can be associated with microcalcifications on mammography.

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Gross Description

Appearance: There are no specific gross findings.
Characteristics: Gross findings are not specific for this microscopic diagnosis.
Size Location: Gross findings are not specific for this microscopic diagnosis.
Multifocality: Often multifocal.

Microscopic Description

Histological Features:
-The ducts and lobules are filled with a proliferation of a mixed population of epithelial and myoepithelial cells
-The cells are arranged in a haphazard or streaming pattern, with irregular, slit-like secondary lumens.
Cellular Characteristics:
-The cells are heterogeneous, with variable sizes and shapes
-The nuclei are oval to spindle-shaped, with fine chromatin and inconspicuous nucleoli
-There is nuclear overlapping.
Architectural Patterns:
-Streaming, swirling, and bridging of cells are characteristic.
Grading Criteria: This is a benign lesion.

Immunohistochemistry

Positive Markers:
-UDH shows a mosaic or mixed pattern of staining for cytokeratins, including high molecular weight cytokeratins like CK5/6
-ER staining is typically weak and heterogeneous.
Negative Markers: Not typically required for diagnosis.
Diagnostic Utility: IHC for CK5/6 is very useful to differentiate UDH from atypical ductal hyperplasia (ADH) and low-grade DCIS.
Molecular Subtypes: Molecular subtyping is not relevant for this benign condition.

Molecular/Genetic

Genetic Mutations: UDH is a polyclonal proliferation.
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 treatment is required.

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.
Diagnostic Challenges: The main challenge is distinguishing florid UDH from ADH or low-grade DCIS.
Rare Variants: There are no specific rare variants.

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]