Anastrozole is an option for women with ductal carcinoma in situ

By John Murphy, MDLinx
Published December 14, 2015

Key Takeaways

Anastrozole is as effective as tamoxifen for treating ductal carcinoma in situ (DCIS) and offers a new option for postmenopausal women with this breast cancer, according to study results presented November 11, 2015 at the San Antonio Breast Cancer Symposium, in San Antonio, TX, and published simultaneously in The Lancet.

“We found that anastrozole and tamoxifen had similar overall efficacies, with slightly better outcomes for those who took anastrozole,” said lead author Jack Cuzick, PhD, Director of the Wolfson Institute of Preventive Medicine and Head of the Centre for Cancer Prevention Queen Mary University of London, in London, UK.

“But more importantly,” he added, “because of their very different side effects, anastrozole can be offered as an alternative for patients who may not tolerate tamoxifen as well or have previous illnesses making tamoxifen unsuitable.”

Up to 20% of all newly diagnosed breast cancers are ductal carcinomas in situ. Tamoxifen has been shown to significantly reduce the risk of breast cancer developing in these women, but the drug's side effects can be difficult.  

In this study (the International Breast Cancer Intervention Study-II DCIS), researchers compared the efficacy of tamoxifen with that of anastrozole in postmenopausal women with hormone-receptor-positive DCIS. Researchers enrolled 2,980 women with DCIS from 236 centers in 14 countries, and randomly assigned them to receive either 1 mg oral anastrozole or 20 mg oral tamoxifen every day for 5 years after surgery.

After a median follow-up of 7.2 years, 144 participants developed breast cancer. Researchers found no clear differences in efficacy between the two treatments—patients in the two groups had statistically similar rates of overall recurrence (67 recurrences for anastrozole vs 77 for tamoxifen). A total of 69 patients died during the course of the study; of these, four deaths were due to breast cancer.

The number of women reporting any adverse event was similar between anastrozole (91%) and tamoxifen (93%), but the side effect profiles of the two drugs differed. Patients who took anastrozole had fewer womb and ovarian cancers and non-melanoma skin cancers, and fewer deep vein thromboses and gynecological issues, compared with those who took tamoxifen. However, patients on anastrozole had more strokes, fractures, and musculoskeletal issues than those on tamoxifen.

“Now we know that anastrozole is effective for treating hormone sensitive ductal carcinoma in situ, women will have a greater choice of treatments to suit their own previous medical histories and tolerability of medications,” Dr. Cuzick said.

The researchers acknowledged that the trial was limited by its lower-than-expected event rate, which adds uncertainly about the lack of statistical significance of some of the small differences seen. They noted that it’s too early to assess the effect of these treatments on mortality, but they’re planning further research with longer-term follow-up to study these issues.

“In summary, anastrozole offers another option for postmenopausal women with ER-positive DCIS, and the choice between it and tamoxifen will probably depend more on previous history of other conditions (e.g., osteoporosis and venous thrombosis) and short-term tolerability (musculoskeletal, vasomotor, and gynecological symptoms) than differences in efficacy,” the authors concluded.

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