Higher Rates of Anastrozole Compared with Tamoxifen
There is the big fuss about DCIS and people are thinking of adding more therapies first of all to it, because there is a new one. DCIS is a risk factor for surgery. So, to keep it from coming back or from escalating to invasive cancer with the possibility of metastases seems a sensible thing if you have a safe and effective way of doing that.
Twenty years ago there was a study with Tamoxifen and against no treatment showing that it helped to prevent recurrences and helped to prevent the incidence of invasive cancer. And that's a good idea. Now, Anastrozole is a class of drugs that looks like it might be better, because it's a better suppression of estrogen signaling. And it might be safer, and the study was done to establish that.
In this study they took women with DCIS, who had been treated by breast conserving surgery and radiation, and they randomly assigned them to receive either Tamoxifen or Anastrozole in a double-blind fashion. So, the women didn't know which pill was which. It was found that the Anastrozole produced a better protection against the occurrence of cancer. It was, probably, a better safety profile, although there were some nuances.
The level of additional protection given by Anastrozole was different for women, who were younger than 60, where the hazard rate was about 0.5 with a good p-value. In women, who were older than 60, Tamoxifen and Anastrozole were equivalent. Of course, they were all postmenopausal women.
In general, women with DCIS are treated with Tamoxifen after surgery. It's beneficial. Now there is another drug, another option for women, where, perhaps, the side effects are a consideration, like a person with a history of thromboembolism or someone, who's worried about uterine cancer. Anastrozole can be used without those problems. It doesn't carry those problems.
Side-effects of Anastrozole Compared with Tamoxifen
Anastrozole tends to produce more fractures, because it's depriving women of estrogen. And Tamoxifen tends to strengthen bones, if it has an estrogenic activity. So, the difference is slight. It was not statistically significant, although, it's numerically different.
The first lesson is that in ten years of follow-up 90% of the patients, who took Anastrozole, are still well. So, the difference is a little more than 90 vs. a little less than 90. But it is a statistically significant and useful difference. It is wise to give some adjuvant therapy in the sense of cancer prevention, because we're much more worried about invasive cancer than a recurrence of DCIS. And that Anastrozole has a safer profile.
In terms of adjuvant therapy for DCIS Anastrozole prevents invasive cancer, which is important, and it has a safer profile in terms of adverse events.