What is invasive ductal carcinoma in an adult female patient?

What is Invasive Ductal Carcinoma?

Invasive ductal carcinoma (IDC) is a malignant epithelial neoplasm of the breast with ductal differentiation that has penetrated through the ductal basement membrane into the surrounding breast tissue, representing the most common type of breast cancer in women. 1, 2

Pathologic Definition and Characteristics

IDC is defined as a malignant epithelial neoplasm that demonstrates ductal differentiation, primarily identified by gland formation at the light microscopic level, and has breached the basement membrane of the ductal system. 1 The tumor consists of cohesive neoplastic epithelial cells that have escaped the confines of the mammary ductal-lobular system and invaded the surrounding stroma. 1

Key Distinguishing Features from DCIS

• IDC differs fundamentally from ductal carcinoma in situ (DCIS) by the presence of invasion through the basement membrane—DCIS remains confined within the ductal structures, while IDC has broken through this barrier. 1, 3
• The transition from DCIS to IDC requires breaching both the basement membrane and the surrounding myoepithelial cell layer. 4
• Approximately 25.9% of DCIS cases detected on core-needle biopsy are upstaged to invasive cancer at surgical excision, indicating occult invasion was present but not sampled initially. 1

Clinical Presentation and Epidemiology

• IDC accounts for the vast majority of invasive breast cancers in adult women, making it the most common histologic subtype. 1, 2
• The tumor typically presents as a palpable mass, mammographic abnormality, or architectural distortion on imaging studies. 1
• IDC is associated with a characteristic intense desmoplastic (fibroinflammatory) reaction in the surrounding stroma, which distinguishes it from in situ disease. 1

Histologic Grading System

The Elston modification of the Bloom-Richardson grading scheme is the standard approach, evaluating three components to assign an overall grade: 1

• Well-differentiated (Grade 1): Forms well-defined glands with cuboidal to columnar cells, basally oriented uniform nuclei, minimal pleomorphism, and rare mitoses. 1
• Moderately differentiated (Grade 2): Shows disorganized growth with less well-defined glands, more prominent nuclear pleomorphism, larger irregular nucleoli, and more frequent mitoses. 1
• Poorly differentiated (Grade 3): Demonstrates small poorly defined glands, individual infiltrating cells, solid areas, marked nuclear pleomorphism with bizarre nuclei, large multiple irregular nucleoli, and numerous atypical mitoses. 1

Prognostic Factors and Risk Stratification

Essential pathologic features that determine prognosis and treatment include: 1

• Tumor size measured in three dimensions
• Histologic type and grade using standardized grading systems
• Lymph node status including number of positive nodes and extracapsular extension
• Resection margin status with distance from tumor to margins
• Hormone receptor status (estrogen and progesterone receptors)
• HER2 receptor expression by immunohistochemistry
• Presence of lymphovascular invasion

Impact of Specific Features

• High histologic grade tumors show approximately 10-15% increased risk of recurrence at 5 years compared to low-grade tumors, though this finding has not been consistent across all studies. 1
• Vascular or lymphatic invasion, tumor necrosis, and inflammatory infiltrate are associated with somewhat increased recurrence risk. 1
• The histologic subtype of invasive ductal carcinoma (as opposed to special types like tubular or mucinous) does not independently affect recurrence risk. 1

Treatment Implications

• Breast-conserving surgery with radiation therapy achieves equivalent survival to mastectomy for early-stage IDC when negative margins can be obtained. 5, 6
• Radiation therapy after breast-conserving surgery reduces local recurrence risk by approximately two-thirds. 5, 6
• Adjuvant systemic therapy decisions are based on tumor biology including hormone receptor status, HER2 status, tumor size, grade, and nodal involvement. 5, 6
• For hormone receptor-positive IDC, tamoxifen 20 mg daily for 5 years is indicated, reducing contralateral breast cancer incidence by 47% with 5 years of treatment. 7

Common Pitfalls in Diagnosis

• Frozen section examination should be avoided for small or mammographically detected lesions, as freezing artifact can obscure small foci of invasion and render tissue uninterpretable. 1
• Margin assessment is critical—positive margins typically require re-excision, and the definition of "positive" varies among institutions but generally means tumor at the inked margin. 1
• The presence of an extensive intraductal component (DCIS comprising ≥25% of the invasive tumor plus DCIS in surrounding tissue) indicates more extensive disease than clinically apparent, but with negative margins does not independently increase recurrence risk. 1