Editing Paget disease of the nipple (section)

== Pathophysiology ==

* Paget cell - large, pale-staining cell with round or oval nuclei and large nucleoli located between the normal keratinocytes of the nipple epidermis
* Theories of development
** Epidermotropic - perhaps more likely - Paget cells spread into the lactiferous sinuses under the nipple and upward to invade the overlying epidermis of the nipple
** In-situ transformation - less likely
* Paget cells do not invade through the basement membrane, and are categorised as carcinoma-in-situ
* Commonly associated with an underlying breast cancer, often in the large sinuses just under the nipple
** Most likely HER2+ and hormone negative
** 90% IDC, 10% DCIS