Post-menopausal women with hormone receptor-positive early-stage breast cancer who take hormone therapy for ten years reduce the risk of their cancer recurring by 34% compared with those who take it for five years, according to the results of a clinical trial.
However, women given the longer-term hormone therapy experience more side effects usually associated with the menopause, such as night sweats and hot flushes, than women who received a placebo, a second study that analysed the women’s quality of life found.
In the first study
, researchers set out to discover whether extending aromatase inhibitor (AI) therapy in women diagnosed with hormone receptor-positive early breast cancer from the traditional five years to ten years had an impact on breast cancer recurrence. The AI chosen for the trial was letrozole.
A total of 1,918 women were enrolled and followed up at 75 months, on average. All of the women recruited were post-menopausal and had already received five years of AI therapy either as their initial treatment or after treatment with tamoxifen.
At follow up after five years, 95% of women given letrozole and 91% of women in the placebo group were breast cancer free (hazard ratio [HR] 0.66; P=0.01). The annual incidence rate of contralateral breast cancer was 0.21% for women in the letrozole group compared with 0.49% for women given placebo (P=0.007), indicating a breast cancer prevention effect if AI treatment is extended.
“Women with early-stage hormone-receptor positive breast cancer face an indefinite risk of relapse,” says lead researcher Paul Goss, director of breast cancer research at Massachusetts general hospital, Boston, Massachusetts, and professor of medicine at Harvard Medical School. “The study provides direction for many patients and their doctors, confirming that prolonging AI therapy can further reduce the risk of breast cancer recurrences. Longer AI therapy also showed a substantial breast cancer preventative effect in the opposite, healthy breast.”
In the second study
, researchers from the same research group looked at the impact of extending letrozole on women’s quality of life.
According to the quality of life indicators used, they found that there was no overall difference in the scores of both groups at 12 months and 36 months.
However, when they looked at menopause-specific quality of life indicators, they found that women in the letrozole group reported worse vasomotor symptoms (P=0.02 at 12 months and P=0.03 at 36 months) and worse sexual functioning (P=0.01 at 12 months and P=0.01 at 36 months) than women in the placebo group.
“The data indicate that continuation of AI therapy after five years prior treatment is not associated with a deterioration of overall quality of life. Treatment related vasomotor and sexual functioning alterations occur with ongoing treatment,” they say.
The results of the study were welcomed by UK patient charity Breast Cancer Now. Chief executive Baroness Delyth Morgan says: “This is a really important study that could one day have a major impact on how we use anti-hormone breast cancer treatments.”
The benefits, in terms of reducing the chances of cancer returning, are similar to those already associated with the hormone therapy tamoxifen, according to the charity.
But Morgan adds: “While this trial showed short-term benefits for patients by doubling the course of standard treatment, we now need to understand the long-term impacts on their survival.
“How this treatment extension might affect a patient’s quality of life also needs to be investigated before we can consider asking women to live with the side effects of treatment for an additional five years.”
The results of the studies were presented at the annual conference of the American Society of Clinical Oncology (ASCO) in Chicago on 5–6 June 2016.
 Goss PE, Ingle JN, Pritchard KI et al. A randomized trial (MA.17R) of extending adjuvant letrozole for 5 years after completing an initial 5 years of aromatase inhibitor therapy alone or preceded by tamoxifen in postmenopausal women with early-stage breast cancer. J Clin Oncol 34, 2016 (suppl; abstr LBA1). Presented at the American Society of Clinical Oncology annual meeting on 5 June 2016. Abstract available at: http://abstracts.asco.org/176/AbstView_176_164642.html (accessed 9 June 2016)
 Lemieux J, Goss PE, Parulekar WR et al. Patient-reported outcomes from MA.17R: A randomized trial of extending adjuvant letrozole for 5 years after completing an initial 5 years of aromatase inhibitor therapy alone or preceded by tamoxifen in postmenopausal women with early-stage breast cancer. J Clin Oncol 34, 2016 (suppl; abstr LBA506). Presented at the American Society of Clinical Oncology annual meeting on 6 June 2016. Abstract available at: http://abstracts.asco.org/176/AbstView_176_168693.html (accessed 9 June 2016)