CYP19A1 and breast cancer: In patients who had an aromatase inhibitor-based endocrine treatment during their first 5 years of therapy, the extension of therapy to 10 years by 5 further years of an aromatase inhibitor (NSABP B-42, MA.17R) did not result in an increased overall survival, and differences in disease-free survival events in favor of longer treatment were often caused by contralateral breast cancers.