(1994–1995). Data shown are the ratio of hospital referral region (HRR) rates of mastectomy for breast cancer to the US average (This figure reproduced with permission from Kristen Bronner, Dartmouth Atlas Project).

Mastectomy among hospital referral regions (HRRs) (1994–1995). The rates varied from 1.1 to 4.0 per thousand female Medicare enrollees, after adjustment. Each point represents one of the 306 HRRs in the United States (This figure reproduced with permission from Kristen Bronner, Dartmouth Atlas Project).

Two clinical scenarios, both with a 30% relative risk reduction in ipsilateral breast tumor recurrence using tamoxifen after surgical treatment for DCIS, but with two different reductions in absolute risk because of differences in baseline recurrence risks. Scenario 1 has a 15% risk of recurrence after breast-conserving surgery with radiation, with five of 100 women benefiting from tamoxifen treatment. Scenario 2 has a 1.4% risk of recurrence after mastectomy, with less than one in 100 women treated with mastectomy benefiting from tamoxifen treatment. This figure represents recurrence risk. These scenarios do not take into account the effects of tamoxifen on contralateral breast cancer risk.