The following article features coverage from the 2020 San Antonio Breast Cancer Symposium. Click here to read more of Cancer Therapy Advisor‘s conference coverage.

Long-term data on ductal carcinoma in situ (DCIS) from the IBIS-II DCIS trial showed that anastrozole and tamoxifen have comparable efficacy, but different safety profiles in postmenopausal women with hormone receptor–positive disease. The long-term results were presented at the 2020 Virtual San Antonio Breast Cancer Symposium (SABCS).

The IBIS-II trial included postmenopausal women with hormone receptor–positive DCIS, atypical hyperplasia, or lobular carcinoma in situ, and randomized 1471 women to receive anastrozole and 1509 to receive tamoxifen for 5 years ( Identifier: NCT00072462).

After a median of nearly 12 years of follow-up, patients who received anastrozole had the same rate of any disease recurrence as patients who received tamoxifen (9.7% vs 8.5%; hazard ratio [HR], 0.89; 95% CI, 0.69-1.16; P =.401).

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The rate of disease recurrence similarly did not significantly differ for invasive disease (HR, 0.89; 95% CI, 0.64-1.24; P =.48) or DCIS (HR, 0.88; 95% CI, 0.56-1.37; P =.56).

The rate of all-cause mortality was also not significantly different between the anastrozole group and the tamoxifen group (odds ratio [OR], 0.93; 95% CI, 0.64-1.35), and neither was the rate of death from breast cancer.

The side-effect profiles for anastrozole and tamoxifen did, however, have clear differences.

Although gynecological cancers were rare, affecting 5 patients in the anastrozole arm and 21 in the tamoxifen arm, patients who received tamoxifen did have significantly higher odds of developing endometrial cancer (odds ratio [OR], 0.17; 95% CI, 0.02-0.77; P =.0086) or ovarian cancer (OR, 0.17; 95% CI, 0.03-0.96; P =.022).

In contrast, patients who received anastrozole had a significantly higher odds of having a fracture (OR, 1.34; 95% CI, 1.06-1.70; P =.013) or transient ischemic attack (OR, 3.10; 95% CI, 1.07-10.92).

“Although our analysis did not show any significant difference in terms of recurrences between anastrozole and tamoxifen, it really shows that an improved understanding of adverse-event profiles will help patients with hormone receptor–positive ductal carcinoma in situ to make an informed decision regarding their treatment,” said study presenter Ivana Sestak, PhD, Centre for Cancer Prevention, London, United Kingdom.

Disclosures: Dr Cuzick received research grants from AstraZeneca and Cancer Research UK. Dr Howell received honoraria and speaker’s fees from AstraZeneca.

Read more of Cancer Therapy Advisor‘s coverage of the 2020 SABCS meeting by visiting the conference page.


Sestak I, Cuzick J, Bonanni B, et al. 12 year results of anastrozole versus tamoxifen for the prevention of breast cancer in postmenopausal women with locally excised ductal carcinoma in-situ. Presented at: 2020 Virtual San Antonio Breast Cancer Symposium; December 8-11, 2020. Abstract GS2-02.