ER+ Breast Cancer

Study shows clinical benefit of a new way of treating advanced ER+ breast cancer

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breast cancer

A research paper published today in The Lancet Oncology demonstrates that the drug enobosarm, a selective androgen receptor modulator that stimulates the male sex hormone receptor, has anti-tumor effects in estrogen receptor-positive breast cancer patients.

Lead author Professor Carlo Palmieri from the University of Liverpool and The Clatterbridge Cancer Centre NHS Foundation Trust, said, “These results are very encouraging—we have shown that in advanced/metastatic breast cancer the use of enobosarm can result in clinical benefit, and is the first clinical proof that a non-estrogen receptor approach with a selective androgen receptor modulator can result in clinical benefit. This builds on the pre-clinical evidence that we published in Nature Medicine.”

For at least 40 years, treatment of this type of breast cancer has focused on directly targeting and inhibiting the activity of the estrogen receptor. This new study, therefore, tested a completely different approach.

The orally administered drug enobosarm is a selective androgen receptor modulator, which can stimulate androgen receptor activity in breast cancers. The androgen receptor is a tumor suppressor in estrogen receptor positive breast cancer.

The multi-site international study led by Dr. Beth Overmoyer of the Dana-Farber Cancer Institute of Boston U.S. evaluated the efficacy and safety of enobosarm in 136 postmenopausal women with locally advanced or metastatic ER-positive, HER2-negative breast cancer (HER2 is a protein called human epidermal growth factor receptor 2, which promotes the growth of cancer cells). Enobosarm was found to have anti-tumor effects, as well as being well tolerated with no significant impact on quality of life.

“These data support further development and assessment of the efficacy of enobosarm and other agents which stimulate the androgen receptor for the treatment of AR-positive, ER-positive, HER2-negative advanced breast cancer,” according to the research.

Can Elderly Patients with ER+ Breast Cancer Omit Radiation After Lumpectomy? 

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For women who have a lumpectomy or breast-conserving surgery, radiation is a standard element in treatment. And we know from classic studies from the National Surgical Adjuvant Breast and Bowel Project (NSABP) and others that women who have a mastectomy actually have the exact same survival as women who have a lumpectomy, provided that the women who have a lumpectomy additionally receive radiation treatment.[1] The question that arises frequently for older women, typically defined as age 65 or 70 or older, is whether it essential to include radiation therapy? And there have been two studies that have looked at the possibility of omitting radiation treatment in older women with estrogen receptor (ER)–positive breast cancer after lumpectomy. 

The first study, from Cancer and Leukemia Group B (CALGB), was led by Kevin Hughes and compared endocrine therapy alone versus endocrine therapy plus radiation treatment.[2,3]It showed that radiation therapy had no impact on long-term survival. However, women who had radiation treatment did have a lower risk of in-breast recurrence. It went to about 2%, with women who did not have radiation having about a 10% or 12% risk of in-breast recurrence. Again, that’s not overall survival, but it does lower the risk of an event within the breast over the next decade. 

The PRIME II study was a European-based study that also asked a question, can women with ER-positive breast cancer omit radiation after lumpectomy if they are older? And fundamentally, the PRIME II study reached the same conclusion, that there was no impact on overall survival amongst older women, but there was a small decrease in the risk of in-breast recurrence.[4]

So what do we actually do in clinic? For many older women, particularly 75 years and older, I think it’s very comfortable to say that they may omit radiation therapy. The risk of in-breast recurrence is generally low, and there will be no impact on survival. For very vigorous women in their late 60s, early 70s, I think you can also point to these data and say that radiation therapy may lower their risk of in-breast recurrence. And since radiation is generally well tolerated, it can be a good option for such women who have a life expectancy well beyond 10 years. Finally, it’s important to remember that these studies assume that the patient will be taking antiestrogen adjuvant therapy. If there is a reason to believe that the patient will not be taking tamoxifen or an aromatase inhibitor or other appropriate endocrine treatment, then you can’t rely on the endocrine therapy to control in-breast recurrence, and those women should receive radiation treatment after lumpectomy.