Extending therapy with aromatase inhibitors to 10 years in postmenopausal patients with hormone receptor-positive early-stage breast cancer.

This study evaluated the effectiveness and safety outcomes of extending treatment with letrozole (Femara), an aromatase inhibitor, to 10 years in postmenopausal patients with hormone receptor-positive (HR+) early-stage breast cancer (BC). The data showed that extending treatment with letrozole to 10 years significantly improved the disease-free survival rates in these patients.

Breast cancer (BC) is one of the most common cancers affecting women worldwide. Many of these patients have a type of tumor that grows in response to female sex hormones such as estrogen and progesterone. These are called hormone receptor-positive (HR+). Patients with this subtype of BC commonly receive hormone therapy which acts by decreasing the female hormones.

In women of reproductive age, the main hormonal therapy used is tamoxifen (Nolvadex). This treatment works by blocking estrogen from reaching receptors (proteins) on cancer cells. Aromatase inhibitors like letrozole are another type of hormonal therapy that works by lowering estrogen production and is used for treating BC in postmenopausal women. Treatment with an aromatase inhibitor for 5 years as up-front monotherapy or after tamoxifen therapy is the standard treatment of choice for HR+ early BC in postmenopausal women. However, it is unknown if extending treatment with an aromatase inhibitor to 10 years reduces the risk of recurrence (cancer coming back) in postmenopausal women with HR+ early-stage BC.

This study involved 1918 postmenopausal women with HR+ early-stage BC. All patients had previously received 4.5-6 years of letrozole therapy. Most of these women have also received before letrozole, tamoxifen treatment. Patients were randomly assigned into 2 groups. Group 1 included 959 patients who further received letrozole. Group 2 included 959 patients who further received a placebo. The average follow-up time was 6.3 years.

After 5 years, 95% of the patients in group 1 were alive and disease-free compared to 91% of the patients in group 2. Patients in group 1 were 34% more likely to survive without cancer recurrence than patients in group 2.  

After 5 years, 93% of the patients in group 1 were alive compared to 94% of the patients in group 2. No significant difference in overall survival was seen between groups. 

0.21% of the patients in group 1 developed second cancer in the opposite breast compared to 0.49% of the patients in group 2. Patients in group 1 were 58% less likely to develop cancer in the opposite breast compared to those in group 2. 

Patients in group 1 experienced more bone-related side effects (bone pain, bone fractures, and decrease in bone density) than patients in group 2. No significant differences were observed in the quality of life between the 2 groups.

This study concluded that extending treatment with letrozole to 10 years significantly improved the disease-free survival rates in postmenopausal women with HR+ early-stage BC.

This study was funded by the Canadian Cancer Society.