Adverse events could be the deciding factor
“The main take-away from this presentation is that choice of adjuvant endocrine therapy for DCIS should be individualized based primarily on the different side effect profiles of the two medications,” Dr. Moore said.
During the trial, “a significant 34% increase in fractures was observed in women who received anastrozole, compared to tamoxifen [HR, 1.34; P = .013],” Dr. Sestak said.
“We also observed a threefold increase in strokes and transient ischemic attacks with anastrozole, compared to tamoxifen [HR, 3.10; P = .021 for both strokes and transient ischemic attacks],” Dr. Sestak added.
She acknowledged that this finding is inconsistent with what is known about aromatase inhibitors in general. It could be that, rather than anastrozole raising the risk of strokes and transient ischemic attacks, tamoxifen was having a beneficial effect. This could be a result of tamoxifen improving endothelial function by increasing vasodilation, “but it is really not clear what the mechanism is,” Dr. Sestak said.
Also contrary to what is known about tamoxifen was an excess of deaths because of endometrial cancer or ovarian cancers. Wherever possible, the pathology reports had been requested to confirm the cause of death, “so we are pretty sure that they are true ovarian cancers and not some other abdominal tumors,” Dr. Sestak said.
“We did observe very clear differences in terms of adverse events,” she said, adding that “improved understanding of adverse event profiles will help patients with HR-positive DCIS to make an informed decision regarding their treatment.”
The IBIS-II DCIS trial was funded by Cancer Research UK, the National Health and Medical Research Council Australia, Breast Cancer Research Foundation, AstraZeneca, and Sanofi Aventis. Two investigators disclosed relationships with AstraZeneca, and one disclosed a relationship with Cancer Research UK. Dr. Sestak and Dr. Moore had no relevant disclosures.
SOURCE: Sestak I et al. SABCS 2020, Abstract GS2-02.