Definition/General
Introduction:
Encapsulated papillary carcinoma (EPC) is a rare variant of papillary breast cancer, characterized by a large, solitary papillary tumor within a cystic space, surrounded by a thick fibrous capsule
It is considered an indolent, low-grade malignancy.
Origin:
It arises from the ductal epithelium.
Classification:
EPC is a form of in situ carcinoma, but because of its unique behavior, it is often treated as a low-grade invasive cancer
When invasion is present outside the capsule, it is designated as EPC with invasion.
Epidemiology:
It typically affects postmenopausal women
It accounts for about 0.5% of all breast cancers.
Clinical Features
Presentation:
Presents as a palpable, well-circumscribed mass
Nipple discharge can occur.
Symptoms:
A painless breast lump is the most common symptom.
Risk Factors:
The risk factors are similar to those for other types of breast cancer.
Screening:
Mammography shows a well-defined, round or oval mass
Ultrasound shows a complex cystic and solid mass.
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Gross Description
Appearance:
A well-circumscribed, encapsulated, cystic mass containing a friable papillary tumor
The cyst may contain hemorrhagic fluid.
Characteristics:
The size is variable, but can be large.
Size Location:
Usually located in the central part of the breast.
Multifocality:
Usually unifocal.
Microscopic Description
Histological Features:
The lesion is a large, expansile nodule with a thick fibrous capsule
Inside the capsule, there is a papillary carcinoma, typically of low to intermediate grade
The key feature is the absence of a myoepithelial layer within the papillae and at the periphery of the nodule.
Cellular Characteristics:
The cells are monotonous, with low-grade nuclear atypia.
Architectural Patterns:
A complex papillary architecture is characteristic.
Grading Criteria:
Graded as low, intermediate, or high grade based on nuclear features.
Immunohistochemistry
Positive Markers:
The epithelial cells are positive for cytokeratins and are usually ER-positive.
Negative Markers:
The key finding is the absence of myoepithelial markers (e.g., p63, calponin) at the periphery of the nodule, which distinguishes it from a large intraductal papilloma.
Diagnostic Utility:
IHC for myoepithelial markers is essential for diagnosis.
Molecular Subtypes:
Most are of the luminal subtype.
Molecular/Genetic
Genetic Mutations:
Mutations in PIK3CA are common.
Molecular Markers:
No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
EPC without invasion has an excellent prognosis, with a very low risk of recurrence or metastasis
The prognosis of EPC with invasion is determined by the characteristics of the invasive component.
Therapeutic Targets:
Treatment is primarily surgical excision
Endocrine therapy may be used for ER-positive tumors.
Differential Diagnosis
Similar Entities:
Intraductal papilloma
Papillary DCIS
Solid papillary carcinoma.
Distinguishing Features:
Intraductal papillomas have a myoepithelial layer
Papillary DCIS is typically smaller and involves multiple ducts
Solid papillary carcinoma has a solid growth pattern.
Diagnostic Challenges:
The main challenge is to assess the entire periphery of the lesion to rule out invasion.
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]