Müllerian adenosarcoma arising in a subserosal adenomyoma

Müllerian adenosarcomas most commonly arise in the uterine corpus from the eutopic endometrium. Occasionally, they arise in the cervix, vagina, broad and round ligaments, and ovaries and rarely in extragenital sites, usually in association with endometriosis. The authors report a rare case of extraendometrial, intramural adenosarcoma of low grade arising from a subserosal adenomyoma in a 46-year-old woman who presented with vaginal bleeding. No evidence of eutopic endometrial origin was identified; the adenosarcoma showed only limited myometrial invasion and no serosal involvement. Because of its subserosal location, the tumor would be overstaged as IC (deeply myoinvasive) in the new FIGO staging system. Stage IC tumors would normally be considered for adjuvant treatment, which would be inappropriate in this case. To avoid overstaging and inappropriate treatment, it is important to recognize that adenosarcoma can, rarely, arise in adenomyomas (or adenomyosis).