On breast core needle biopsy, a 45-year-old woman's specimen shows cells with large nuclei, prominent nucleoli, and high mitotic rate filling distended ducts with central necrosis and periductal stromal fibrosis. There is no stromal invasion identified. The Ki-67 proliferation index is 80%. ER/PR are negative. HER2 is 3+. This lesion is best classified as:
- A Invasive ductal carcinoma (IDC) grade 3, HER2-enriched molecular subtype
- B Ductal carcinoma in situ (DCIS), nuclear grade 3 (high-grade), HER2-overexpressing subtype, with comedo necrosis ✓
- C Lobular carcinoma in situ (LCIS), pleomorphic variant with central necrosis
- D Encapsulated papillary carcinoma with fibrovascular cores and necrosis
Explanation
The description fits DCIS (ductal carcinoma in situ): malignant epithelial cells filling and expanding ducts with central comedo necrosis (characteristic of high-grade DCIS), but NO stromal invasion. DCIS is classified by nuclear grade (1-3) and architectural pattern (comedo, cribriform, micropapillary, solid, papillary). Nuclear grade 3 DCIS shows large nuclei >2.5x RBC diameter, prominent nucleoli, numerous mitoses. Comedo necrosis with periductal fibrosis and calcification is typical of high-grade DCIS. HER2 3+ and ER/PR-negative are consistent with HER2-enriched molecular subtype. This distinction from IDC is critical as DCIS has excellent prognosis and is managed with excision +/- radiotherapy; IDC would require systemic therapy consideration.
Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.
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Written and medically reviewed by the StethoPrep medical team.