What is Ductal Carcinoma In Situ (DCIS)?

What is Ductal Carcinoma In Situ (DCIS)?

DCIS is a heterogeneous group of neoplastic lesions confined to the breast ducts that have not invaded beyond the ductal basement membrane—essentially, it represents abnormal cells inside the milk ducts that have not spread into surrounding breast tissue. 1

Clinical Significance and Epidemiology

• DCIS is a non-obligate precursor to invasive breast cancer, meaning not all cases will progress to invasive disease if left untreated. 2, 3
• Before widespread mammography screening, DCIS was uncommon, accounting for only 2-3% of palpable breast cancers. 1
• Currently, DCIS accounts for approximately 20% of all breast cancers diagnosed in the United States due to screening mammography. 1, 4
• The prognosis is excellent, with 10-year overall survival rates of 97.2% to 98.6%. 1

How DCIS Presents

• DCIS most commonly presents as a mammographically detected, clinically occult (non-palpable) disease. 1
• The hallmark mammographic finding is microcalcifications in 90-98% of cases. 1
• These calcifications are typically pleomorphic (varying in size, form, and density), often arranged in linear or segmental patterns. 1
• Approximately 10% of cases present as an uncalcified mass on mammography. 1
• Definitive diagnosis requires pathologic evaluation of tissue, as imaging alone cannot determine whether the basement membrane has been breached. 1

Pathologic Classification

The classification of DCIS has evolved significantly:

• Traditional classification was based on architectural patterns (comedo, cribriform, micropapillary, papillary, and solid subtypes), but this system was developed when all DCIS was treated with mastectomy and had limited clinical utility. 5
• Modern classification systems prioritize nuclear grade and the presence or absence of necrosis, as these features correlate with risk of recurrence. 5
• High nuclear grade and extensive comedonecrosis are associated with higher risk of early local recurrence following breast-conserving therapy. 5
• A 1997 consensus conference recommended that pathology reports should clearly state nuclear grade, presence or absence of necrosis, cell polarization, and architectural patterns. 5

Critical Pathologic Features

The pathology report should include specific elements that guide treatment decisions:

• Margin status is arguably the most important aspect—DCIS extending to surgical margins typically requires further surgery. 5
• Extent (size) of DCIS, though difficult to measure precisely in non-palpable lesions. 5
• Nuclear grade, which shows the greatest consistency among pathologists when classifying DCIS. 5
• Presence and extent of necrosis. 5
• Architectural patterns, as micropapillary subtypes may involve multiple quadrants independent of nuclear grade. 5

Risk of Progression

• If left untreated, approximately 12% of DCIS lesions progress to invasive ductal carcinoma. 6
• Following breast-conserving therapy, about 50% of recurrences are invasive cancer and 50% are DCIS. 1, 7
• Risk factors for progression include larger lesion size, younger age, and HER2 overexpression. 1

Key Distinction from LCIS

• Lobular carcinoma in situ (LCIS) is fundamentally different—it is an incidental finding considered a marker of increased bilateral breast cancer risk rather than a malignant lesion requiring surgical excision. 5
• Unlike DCIS, the relationship between LCIS and surgical margins is not clinically important. 5
• The increased risk from LCIS applies to both breasts and is probably lifelong. 5

Common Pitfall

• A meta-analysis found that 25.9% of cases diagnosed as DCIS on core biopsy are upstaged to invasive cancer at surgical excision, highlighting the importance of complete surgical excision even for what appears to be "pure" DCIS. 1