Ductal Carcinoma

DCIS (ductal carcinoma in-situ): Malignant luminal epithelial cells proliferating within the duct, myoepithelial layer intact. Graded by nuclear grade and the presence of comedo necrosis (central necrosis with calcification — higher grade, more likely to progress). DCIS is a non-obligate precursor to invasive disease — not all DCIS progresses, and this is the crux of the overdiagnosis debate in screening.

Invasive ductal carcinoma, no special type (NST): ~70–80% of cases. This is essentially the default category — it doesn't show enough specific features to classify as a special type. Variable morphology, graded using the Nottingham system (tubule formation, nuclear pleomorphism, mitotic count → grade 1–3).