Notably, several case reports indicated promising efficacy of antiestrogen therapy6 or anti-HER2 targeted therapies in EMPD,7–10 suggesting that breast cancer treatment strategies may also guide EMPD treatment; however, the rarity of the disease and consequent lack of a biological basis warrant comprehensive molecular and biological profiling of clinical EMPD to facilitate its appropriate management. Here, ERBB2 is linked to extramammary Paget disease.