Aromatase inhibitors versus tamoxifen following chemotherapy for perimenopausal women with breast cancer

This study was carried out to assess the use of aromatase inhibitors (AI) versus tamoxifen (Novaldex) for women before menopause with estrogen receptor-positive (ER+) breast cancer (BC). The authors found that AIs were associated with better outcomes than tamoxifen in these patients. 

About 80% of all BCs are ER+. This means the cancer cells grow in response to the hormone estrogen. These patients are commonly treated with chemotherapy to kill cancer cells followed by hormonal therapy to keep the cancer from coming back. Hormonal therapy choice depends on the reproductive status of women.

In women of reproductive age, the main hormonal therapy used is tamoxifen. This treatment works by blocking estrogen from reaching receptors (proteins) on cancer cells. An alternative hormonal treatment is AI such as anastrozole (Arimidex) or letrozole (Femara). AIs reduce the amount of circulating estrogen in the body in order to reduce the growth of ER+ cancer cells. AIs are mainly used in postmenopausal women, who already have lower quantities of estrogen in the body.

The menopausal transition phase (perimenopause) is the period usually after 45 years of age when the body transitions to menopause. During this period, women can have irregular menstrual cycles and menopausal symptoms such as hot flashes. Women aged 40 or older with BC can enter the menopausal transition after chemotherapy. It is unclear if tamoxifen or AIs are a better hormonal treatment after chemotherapy in these women. 

There were 2295 women aged 45-50 years with ER+ BC involved in this study. All patients were treated with chemotherapy followed by hormonal therapy. Most patients received different types of hormonal therapy. 82.9% of patients started on tamoxifen. 34.7% of patients received only one type of hormonal therapy (56.3% – tamoxifen and 43.7% – AIs). The average follow-up was 7.6 years. 

Patients who received an AI treatment for more than 75% of the time had a 36% higher survival without recurrence compared to patients who received mostly tamoxifen (AIs in less than 25% of the time). Women who received AIs between 25% and 75% of the time had a similar survival without recurrence with those who received AIs less than 25% of the time. Every 10% increase in AI treatment time reduced the rate of recurrence by 5%.

The overall survival rate was also improved in women who received AIs for more than 75% of the hormonal therapy time. 

The authors concluded that perimenopausal women with ER+ BC had a significant benefit from a longer period with AI treatment versus tamoxifen following chemotherapy.

The exact menopausal status of the patients before chemotherapy was unknown. Also, information about adherence to treatment was not known. This might have influenced the results.