A federally funded phase III trial suggests that postmenopausal women with ductal carcinoma in situ (DCIS) may have an additional option for breast cancer prevention.

The study compared the standard five-year treatment of tamoxifen to five years of the aromatase inhibitor anastrazole in more than 3,000 DCIS survivors.

The 10-year breast cancer-free survival rates were higher in the anastrazole group than in the tamoxifen group (93.5% vs. 89.2%).

“The good news is tamoxifen and anastrazole are both very effective, but it seems that women have better chances of staying well with anastrazole,” said lead study author Richard G. Margolese, MD, a professor of surgical oncology at The Jewish General Hospital, McGill University in Montreal, Canada.

“Women should also consider differences in side effects when discussing treatment options with their doctors.”

Women with DCIS are at increased risk of developing invasive breast cancer, although breast cancer-related death is uncommon following DCIS treated with radiation and lumpectomy.

While both tamoxifen and aromatase inhibitors have been used to prevent recurrences of more advanced forms of breast cancer, this is the first study to compare the two treatments in women with DCIS.

In the study, 3,104 postmenopausal patients with hormone receptor-positive DCIS were randomly assigned to daily tamoxifen or anastrazole, each given for five years.

Prior to starting hormone therapy, all had undergone lumpectomy and radiation therapy.

After an average follow-up period of 8.6 years, 114 breast cancers were detected in the tamoxifen group compared to 84 in the anastrazole group.

This included recurrences of DCIS as well as development of a new breast cancer (DCIS or invasive) in the same or other breast.

The 10-year breast cancer-free rates were higher in the anastrazole group than in the tamoxifen group (93.5% vs. 89.2%), and this difference was statistically significant.

There were eight deaths due to breast cancer in the tamoxifen group and five in the anastrazole group.

While the 10- year overall survival rates were comparable in the two groups (92.5% for anastrazole and 92.1% for tamoxifen), a subgroup analysis revealed that anastrazole may not be superior to tamoxifen in women older than 60 years.

Hormone receptor-positive breast cancer is dependent on oestrogen for growth.

Tamoxifen and anastrazole block the oestrogen growth signal in different ways.

While tamoxifen blocks the oestrogen receptor (i.e., access of oestrogen to the cancer cells), anastrazole suppresses the manufacturing of oestrogen.

Generally, there were no significant differences in the toxicity profiles of these agents.

The main side effect of anastrazole is hastening of osteoporosis, which increases the risk of bone fracture.

Indeed, anastrazole resulted in a higher rate of bone fractures compared to tamoxifen, though the difference was not statistically significant.

In addition, treatment with tamoxifen was associated with higher rates of uterine cancer, though the difference also did not reach statistical significance.

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Source: ASCO