Real-World Data Back Up Adjuvant Endocrine Therapy For Contralateral Breast Cancer Prevention

A clinical practice study finds an association between adjuvant tamoxifen or aromatase inhibitor treatment and reduced risk of contralateral breast cancer, in line with prior clinical trial data

medwireNews: Long-term adjuvant endocrine treatment, either with tamoxifen or aromatase inhibitors (AIs), reduces the risk of a contralateral tumour in women with invasive breast cancer, shows research conducted in a general community setting.

Editorialists Balkees Abderrahman and V Craig Jordan, both from the University of Texas MD Anderson Cancer Center in Houston, USA, comment that the findings are “reassuring because all the rules derived, until now, from randomized clinical trial overview analyses hold true.”

During a median follow-up of 6.3 years, contralateral breast cancer (CBC) developed in 248 of 7541 patients treated for a primary invasive breast tumour at two US medical centres between 1990 and 2008.

Compared with nonusers, current and former users of tamoxifen had a reduced risk of developing CBC, with the risk progressively declining with increasing duration of treatment. For instance, among women currently receiving tamoxifen, the CBC risk was a significant 51% lower with between 1 and 4 years of use than nonuse, while it was 74% lower with at least 4 years of treatment.

Furthermore, for every year of tamoxifen use, the risk of CBC was a significant 24% lower among current versus never users. And although “risk reductions were slightly smaller” for past tamoxifen users – with, for example, a 15% reduction for every year of use for women who stopped treatment at least 5 years previously – the decreases were significant, the researchers note.

The findings were similar for women with oestrogen receptor (ER)-positive breast cancer, but not for those with an initial diagnosis of ER-negative disease, among whom adjuvant tamoxifen treatment did not lead to a reduction in the CBC risk.

Using data from participants with ER-positive breast cancer who survived for at least 5 years, the study authors estimate that 4 or more years of tamoxifen therapy will prevent three CBCs per 100 women in the 10 years following the primary diagnosis.

Lead investigator Gretchen Gierach, from the National Cancer Institute in Bethesda, Maryland, USA, and co-workers also found that adjuvant AI therapy without tamoxifen reduced the risk of developing CBC, with a significant 52% decrease per year of use relative to nonuse. However, they were unable to evaluate the effects of individual drug classes and varying durations of therapy as AIs were only recently introduced into clinical practice at the study centres.

In conclusion, the team emphasises that “[i]f adjuvant endocrine therapy is indicated for breast cancer treatment, these findings in concert with trial data suggest that women should be encouraged to complete the full course.”

The editorial authors believe that the conclusion “is even more important because in the future adjuvant endocrine therapy will last for 10 years.”

However, the key issue is adherence, the lack of which leads to not only early relapse and increased medical costs, but also a poorer quality of life, they say.

“Simply stated, no medicine, no benefit”, the editorialists conclude in JAMA Oncology.


Gierach GL, Curtis RE, Pfeiffer RM, et al. Association of adjuvant tamoxifen and aromatase inhibitor therapy with contralateral breast cancer risk among US women with breast cancer in a general community setting. JAMA Oncol; Advance online publication 6 October 2016. doi: 10.1001/jamaoncol.2016.3340

Abderrahman B, Jordan VC. Long-term adjuvant tamoxifen therapy and decreases in contralateral breast cancer. JAMA Oncol; Advance online publication 6 October. doi: 10.1001/jamaoncol.2016.3324

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