The study helps address an important question about the duration of AI use. Aromatase inhibitors such as Arimidex lower estrogen levels by preventing aromatase, an enzyme found in fat tissue, from changing other hormones into estrogen. The medication is prescribed to women with hormone-receptor-positive breast cancer (meaning their cancer grows in response to the presence of estrogen) after their initial phase of treatment in order to help prevent cancer recurrence. “There have been several studies showing that expanding the duration of treatment [after the initial five years] is beneficial. But what is not known is for how long,” says the lead author of the study, Michael Gnant, MD, the director and chairman of the department of surgery at the comprehensive cancer center at the Medical University of Vienna. As a result, “people vary in what they recommend,” says Dr. Gnant. The question is important because the medications are not easy to take, and have been associated with a range of side effects, such as joint pain, hot flashes, sexual dysfunction, hair loss, and an increased risk of bone fracture. In some women, the side effects are debilitating and even cause some to quit taking the drugs.
New Study Provides Surefooted Guidance
In the largest and most powerful study of this issue to date, Gnant and his colleagues analyzed data from 3,484 women who began taking aromatase inhibitors between February 2004 and June 2010. All the women had received five years of AI or other endocrine therapy, such as Soltamox (tamoxifen). In the randomized, controlled study, they were assigned to take Arimidex for either two additional years or five additional years. At the conclusion of the study, on June 30, 2016, 22 percent of the women in the two-year group and 22 percent of the women in the five-year group had their breast cancer recur. There were also no significant differences in overall survival or in the time before breast cancer was diagnosed in the other breast (contralateral breast cancer). The results are beyond doubt, says Gnant. “The positive message is that we now know two years is sufficient for almost every patient. This can help avoid unnecessary side effects for many, many women.”
Possible Negatives to Taking AIs for Longer Than Two Years
There were also potential downsides to taking the medication longer than two years. Researchers found that bone fractures were more likely to occur three to five years after the start of therapy, for instance, suggesting that longer AI treatment may increase the risk of fractures. “We have shown an increased risk of bone fractures by about 35 percent in those women who have an additional five years of therapy compared to an additional two years,” Gnant says. “If we avoid unnecessary prolongation of therapy, we can hope these fractures would not occur.”
Answering Remaining Questions
The study only explored the AI Arimidex. However, the AI medications are all similar, and Gnant says he believes the study results would apply to other types, as well. Gnant also said that further research may show that some patients benefit from taking AIs for longer periods. A large, ongoing study could reveal specific genetic markers in patients that indicate whether a longer duration of AI therapy could be useful. In the meantime, women taking AIs should talk to their doctors about how long they need to take the medications, Gnant says. “If you are on adjuvant endocrine treatment you should discuss with your doctor the duration of therapy. Based on individual risks and discussion of all scientific results, patients and physicians should be able to come to a decision about the appropriate length of therapy.”
