Understanding more about the duration of adjuvant hormonal therapy in breast cancer

By: William Peters, M.D., Ph.D.

Two years ago, a large Canadian study in breast cancer concluded that extending adjuvant hormonal treatment of breast cancer from 5 years to 10 years improved disease control for some patients – primarily post-menopausal women with high risk features. However, there was controversy because the effect on disease recurrence was small (4%) and there was no difference in overall survival, and long-term treatment was associated with more side effects. It has long been considered standard to use five years of treatment with anti-estrogen therapy.

Now, a new study (called ABCSG-16) involving near 3,500 women compared 7 years of treatment (2 additional years) with a total of 10 years of treatment (5 additional years) with aromatase inhibitors [anastrazole (Arimidex), letrozole (Femara) or exemestane (Aromasin)]. There was no difference in either disease recurrence or survival between the additional 2 and 5 years and there were more bone fractures and other side effects of treatment with the longer duration. More time will be needed to determine if there is any subgroup of patients for which the longer treatment would be valuable, but there was no evidence of that from the current data. In the first study, it was shown that most of the recurrences were local recurrences and there was no difference in survival among the 5 and 10 year treatment groups. This suggests that patients with small tumors or low-grade tumors may not even need the additional 2 years of treatment, particularly if there is evidence of side effects. I would recommend a careful discussion of the risks and benefits of the duration of treatment with your physician.

While hormone treatment is generally well tolerated, it was clear that there was difficulty in patients complying with the treatment for extended duration as well. In the 2 additional years of treatment group, 20% of patients were not taking their drug by the end of the time, and in the 5 years group, 40% had quit. 

In summary, it looks like 7 years is the maximum time for adjuvant hormonal therapy for post-menopausal women – good news for women with breast cancer.