Ductal Carcinoma In Situ (DCIS) is a non-invasive breast condition where abnormal cells are confined to the milk ducts, classified as a Stage 0 disease. High-Grade DCIS with Microinvasion (HG DCIS-MI) is a specific subtype that bridges the gap between non-invasive and fully invasive breast cancer. This diagnosis occurs when a small number of high-grade ductal cells have broken through the duct wall into the surrounding tissue. The presence of this microinvasion component fundamentally shifts the treatment approach compared to pure DCIS.
Understanding the Diagnosis
The diagnosis of DCIS with Microinvasion is defined by a pathological distinction: the invasive focus must measure 1 millimeter (mm) or less in its largest dimension. If the invasive component is larger than 1 mm, the diagnosis becomes invasive ductal carcinoma, which has a different staging and treatment pathway. This tiny breach of the duct’s basement membrane elevates the disease beyond pure DCIS. The “high-grade” component indicates the cells are rapidly dividing and appear highly abnormal under the microscope, often associated with a type of cell death called comedo necrosis. High-grade DCIS has a greater potential for recurrence and progression compared to low- or intermediate-grade DCIS. While the microinvasion is exceedingly small, its presence influences the need for lymph node evaluation.
Primary Surgical Interventions
Surgical removal of the diseased tissue is the initial and most important step in treating HG DCIS-MI, with two main local treatment options available. Breast-Conserving Surgery (BCS), often called a lumpectomy, removes the tumor and a rim of healthy tissue around it. BCS is a suitable choice when the tumor is small relative to the overall breast size, allowing for an acceptable cosmetic outcome.
The goal in all surgical removal is achieving clear or “negative” margins, meaning no cancer cells are found at the edges of the removed tissue. If cancer cells are detected at the margin, a second surgery, known as a re-excision, is typically required to remove additional tissue. Mastectomy, the second option, involves the removal of the entire breast. This is generally recommended if the DCIS is large, involves multiple areas, or if clear margins cannot be obtained with lumpectomy.
Overall survival rates are similar between the two surgical approaches for DCIS. Mastectomy generally eliminates the need for post-operative radiation. Patient preference and the ability to undergo subsequent radiation therapy also factor into the decision.
Axillary Staging
The presence of microinvasion makes evaluation of the axillary (underarm) lymph nodes a necessary consideration in HG DCIS-MI. This staging is performed using a procedure called a Sentinel Lymph Node Biopsy (SLNB). The sentinel node is the first lymph node to which cancer cells are likely to spread from the primary tumor, and it is identified using a radioactive tracer or a blue dye injected near the tumor site.
The risk of finding cancer cells in the sentinel lymph node in DCIS-MI is low, typically reported to be around 5% to 12%. Performing the SLNB is often recommended concurrently with the initial lumpectomy or mastectomy because the procedure is much less complicated at that time. The results of the SLNB are crucial for determining the need for further systemic treatments. If the sentinel node contains a macrometastasis, subsequent removal of additional lymph nodes, called an Axillary Lymph Node Dissection, may be discussed.
Post-Surgical Adjuvant Therapy
Following surgery, adjuvant therapies are often employed to further reduce the risk of recurrence in the breast or the development of new cancer. Radiation therapy is a common post-operative treatment, particularly for patients who have undergone a lumpectomy. Standard external beam radiation is delivered to the remaining breast tissue over several weeks to destroy any microscopic cancer cells.
Radiation therapy after BCS significantly lowers the chance of the cancer returning in the same breast. While generally not necessary after a mastectomy, it is sometimes considered if the tumor was very large or if margins were difficult to achieve. The decision to use radiation depends on factors like the patient’s age, the size of the tumor, and the achieved margin width.
Systemic therapy, known as endocrine therapy, is another major component of the adjuvant plan, specifically for tumors that are hormone receptor-positive (ER/PR+). These treatments work by either blocking estrogen from reaching the cancer cells or by lowering the body’s estrogen levels. Tamoxifen is commonly used for both pre- and post-menopausal women, while Aromatase Inhibitors are typically reserved for post-menopausal women. Endocrine therapy is generally prescribed for five years and reduces the risk of recurrence in the treated breast, as well as lowering the chance of a new cancer developing in the opposite breast.
For high-grade tumors that are hormone receptor-negative and HER2-positive, targeted therapy may be considered, but its role in DCIS-MI is still being studied and is not yet standard across all cases.