Apocrine cystadenoma and apocrine hidrocystoma: examination of 21 cases with emphasis on nomenclature according to proliferative features

Background: Apocrine cystadenoma (AC) and apocrine hidrocystoma (AH) have been used interchangeably in the literature to designate cystic lesions of apocrine glands. Methods: We reviewed 21 cases with biopsies of apocrine cystic lesions diagnosed as AH or AC stained by hematoxylin and eosin. The following histological characteristics were recorded: (a) number of cysts, (b) predominant architectural growth pattern of cyst wall, (c) tumor circumscription, (d) nuclear atypia, (e) mitotic activity, counted per 1 mm(2) and (f) Ki-67 staining pattern. Results: Our findings clearly show that there is a non-proliferative group and a proliferative group among the lesions. In the non-proliferative group, one may see some structures that resemble papillary projections but lack a fibrous core. In the proliferative group, we found true papillae, and this change was associated with atypia, mitotic activity and increased Ki-67 staining. Conclusions: Apocrine cystic lesions with true papillary projections should be referred to as AC rather than AH, to emphasize the proliferative adenomatous growth and depicted by their frequency of cytological atypia and high mitotic activity. Furthermore, we suggest complete excision of AC that are proliferative tumors.