Editing DCIS (section)

== Pathophysiology ==

* Discrete spaces filled with malignant cells, usually with a recognisable basal cell layer composed of presumably normal myoepithelial cells
* Spreads along the 'galactophoric tree' and often is continuous along the branching ductal network
* The malignant cells can invade across the basement membrane, usually recapitulating the morphology of the cells inside the duct
* Microinvasion - breach of the myoepithelial duct boundary by malignant cells, but measuring <=1mm
** It is possible to mistake various structures for microinvasion, including lobules, crush artefacts, and branching ducts
* 90% of DCIS expresses ER and 40% expresses HER2
** Low-grade lesions have higher ER expression
** Progesterone expression tends to correlate with ER
* Timelines for progression to invasion are not fully understood