Dr. Margenthaler further explained that the tumors of women under 40 tended to be estrogen- and progesterone-negative , which often lead to poorer outcomes . That is the case because these tumors do not respond to the antiestrogen therapies now available , such as tamoxifen . Young women also are more likely to carry a gene called HER2NEU , which is found in all the cells of the human body . Some cancers make extra copies of this gene , which also is associated with poorer outcomes , higher rates of recurrence , and metastatic spread .