## DCIS vs IDC: The Critical Distinction **Key Point:** The defining difference between DCIS and IDC is the **integrity of the basement membrane and myoepithelial layer**. DCIS is confined within the duct; IDC breaches these barriers and invades the surrounding stroma. ### Comparative Pathology | Feature | DCIS | IDC | |---------|------|-----| | Basement membrane | Intact | Disrupted/absent | | Myoepithelial layer | Present (may be attenuated) | Absent | | Stromal invasion | No | Yes | | Necrosis | May be present (comedo type) | May be present | | Nuclear grade | Variable (low to high) | Variable (low to high) | | Prognosis | ~1–2% risk of progression if untreated | Requires systemic therapy | **High-Yield:** DCIS is a **non-invasive** lesion confined by the basement membrane. The presence of myoepithelial cells (immunopositive for p63, α-smooth muscle actin) around the lesion confirms DCIS. Loss of this layer = IDC. **Clinical Pearl:** DCIS is often detected on mammography as microcalcifications. The grade (low, intermediate, high) and presence of necrosis guide treatment decisions, but the grade alone does not distinguish DCIS from IDC. **Mnemonic:** **BM-ME rule** — Basement Membrane intact + Myoepithelial layer present = DCIS (confined); Basement Membrane breached + Myoepithelial layer absent = IDC (invasive). ### Why Necrosis Is Not the Discriminator Necrosis (especially comedo-type) is common in high-grade DCIS but can also be seen in IDC. It is a feature of grade, not invasiveness.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.