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]