Definition/General

Introduction:
-Invasive papillary carcinoma is a rare variant of invasive ductal carcinoma characterized by a predominantly papillary architecture
-It is important to distinguish it from other papillary lesions of the breast.
Origin: It arises from the ductal epithelium.
Classification: It is a subtype of invasive ductal carcinoma.
Epidemiology:
-It is rare, accounting for less than 1% of all invasive breast cancers
-It typically affects postmenopausal women.

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 lobulated mass.

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Gross Description

Appearance:
-A well-circumscribed, soft, friable mass
-It may be cystic.
Characteristics: The size is variable.
Size Location: Usually located in the central part of the breast.
Multifocality: Usually unifocal.

Microscopic Description

Histological Features:
-The tumor is composed of papillae with fibrovascular cores that are lined by malignant epithelial cells
-The key feature is stromal invasion by the papillary structures or by individual cells
-The myoepithelial layer is absent in the invasive component.
Cellular Characteristics:
-The cells are typically low to intermediate grade, with mild to moderate nuclear atypia.
Architectural Patterns:
-A complex, branching papillary architecture with stromal invasion is characteristic.
Grading Criteria: Graded using the Nottingham grading system.

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) in the invasive component
-HER2 is usually negative.
Diagnostic Utility: IHC for myoepithelial markers is essential to confirm invasion.
Molecular Subtypes: Most are of the luminal subtype.

Molecular/Genetic

Genetic Mutations: Not well characterized.
Molecular Markers: No specific molecular markers are routinely used for diagnosis.
Prognostic Significance:
-The prognosis is generally better than that of adenocarcinoma NST of similar size and grade
-Lymph node metastasis can occur.
Therapeutic Targets:
-Treatment is similar to that of conventional breast cancer, based on ER and HER2 status.

Differential Diagnosis

Similar Entities:
-Encapsulated papillary carcinoma
-Papillary DCIS.
Distinguishing Features:
-Encapsulated papillary carcinoma is confined by a fibrous capsule
-Papillary DCIS is an in situ lesion confined to ducts.
Diagnostic Challenges: The main challenge is to identify stromal invasion, which can be subtle.
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]