A new study shows that the hard-to-treat, estrogen receptor-negative breast cancer (ER-negative) has been declining steadily since 1992. However, rates of the more common ER-positive breast cancer, showed more variance. From 1992 to 2000, its incidence rose, peaking at 232 cases per 100,000 women. Then, it dropped sharply from 2000 to 2003. Since then, it's been slightly increasing.