Definition/General
Introduction:
An atypical intraductal papilloma is a benign papillary lesion of the breast that contains a focus of atypical ductal hyperplasia (ADH) or low-grade ductal carcinoma in situ (DCIS).
Origin:
It arises from the ductal epithelium.
Classification:
It is classified as a benign proliferative breast lesion with atypia
The presence of atypia within a papilloma increases the risk of subsequent breast cancer.
Epidemiology:
They are uncommon lesions, found in a small percentage of breast biopsies.
Clinical Features
Presentation:
Similar to benign papillomas, they can present with nipple discharge or as a palpable mass.
Symptoms:
Nipple discharge is the most common symptom.
Risk Factors:
There are no well-established risk factors.
Screening:
They can be associated with mammographic abnormalities, such as a mass or calcifications.
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Gross Description
Appearance:
A friable, polypoid mass within a dilated duct.
Characteristics:
The gross appearance is indistinguishable from a benign papilloma.
Size Location:
Usually small and located in the large subareolar ducts.
Multifocality:
Can be multifocal.
Microscopic Description
Histological Features:
The lesion is a papilloma with a focus of epithelial proliferation that meets the criteria for ADH or low-grade DCIS
The atypical proliferation is typically focal and involves the epithelial component of the papilloma.
Cellular Characteristics:
The atypical cells are monotonous, with low-grade nuclear atypia, similar to that seen in ADH or low-grade DCIS.
Architectural Patterns:
The atypical proliferation can have cribriform, micropapillary, or solid patterns.
Grading Criteria:
This is a lesion with atypia
The key is to distinguish it from a papilloma completely involved by DCIS.
Immunohistochemistry
Positive Markers:
The myoepithelial layer is preserved, which can be highlighted by myoepithelial markers
The atypical epithelial cells are ER-positive.
Negative Markers:
The atypical cells are negative for high molecular weight cytokeratins (e.g., CK5/6).
Diagnostic Utility:
IHC for myoepithelial markers is essential to distinguish from invasive papillary carcinoma
CK5/6 can help differentiate the atypical proliferation from usual ductal hyperplasia within a papilloma.
Molecular Subtypes:
Molecular subtyping is not relevant for this pre-invasive lesion.
Molecular/Genetic
Genetic Mutations:
The atypical component can show genetic alterations similar to low-grade DCIS, such as loss of heterozygosity at 16q.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
Atypical papillomas are associated with a significantly increased risk of subsequent breast cancer, higher than that of a benign papilloma or ADH alone.
Therapeutic Targets:
Surgical excision is the standard treatment to ensure the entire lesion is removed and to rule out an associated invasive carcinoma.
Differential Diagnosis
Similar Entities:
Benign papilloma with UDH
Papillary DCIS
Invasive papillary carcinoma.
Distinguishing Features:
UDH within a papilloma has a heterogeneous cell population and mosaic CK5/6 staining
Papillary DCIS involves the entire papilloma and lacks a myoepithelial layer in the papillae
Invasive papillary carcinoma shows stromal invasion.
Diagnostic Challenges:
The main challenge is distinguishing an atypical papilloma from papillary DCIS on a core needle biopsy
The distinction can be difficult and often requires excision for definitive diagnosis.
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]