Research Highlights from the 2021 San Antonio Breast Cancer Symposium

For 2021, top researchers, physicians, manufacturers, and patient advocates met in-person and virtually for the annual San Antonio Breast Cancer Symposium. Once again, this conference shared an abundance of new research on breast cancer from around the globe. Here are some of the highlights:

EARLY-STAGE BREAST CANCER

1. Pembrolizumab shows benefit for patients with high-risk early-stage triple negative breast cancer with PD-L1 expression. Phase 3 of the KEYNOTE-522 study showed positive event-free survival for neoadjuvant pembrolizumab plus chemotherapy followed by adjuvant pembrolizumab.
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2. Trastuzumab biosimilar, Ontruzant, shows equivalent long-term survival data compared to Herceptin. The 5-year overall survival for Ontruzant was 92.5% and 85.4% for the Herceptin group demonstrating comparable long-term safety and efficacy.
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3. In a U.S. based study, researchers found that Black breast cancer patients may receive more modifications in treatment regimens leading to poorer outcomes. In a study exploring treatment modifications made to breast cancer patients receiving neoadjuvant therapy, researchers found that Black patients accounted for 59% of those who received modified treatments. Those who received modified treatment regimens were less likely to achieve pathologic complete response than those who completed standard treatment regimens.
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4. Diabetes drug metformin does not provide benefit for HR positive or negative breast cancer but may show benefit for HER2 positive breast cancer.  In the Phase III CCTGMA.32 trial, for those with HER2 positive breast cancers, invasive disease-free survival and overall survival was improved following adjuvant metformin.
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5. Black women have a higher risk of developing lymphedema after axillary lymph node dissection compared to White women. In a study looking at the rates of lymphedema among Black and White women, researchers found that Black race was also the strongest predictor of lymphedema. 
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METASTATIC BREAST CANCER

1. Elacestrant significantly improved outcomes for men and postmenopausal women with ER+ HER2- metastatic breast cancer. Patients in phase III of the EMERALD trial pretreated with endocrine therapy and CDK4/ inhibitors saw a 30% lower risk of death and an increased progression-free survival compared to patients receiving standard of care in the second or third line setting.
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2. Trastuzumab deruxtecan (T-DXd) improves survival for HER2+ metastatic breast cancer patients, including those with brain metastases. In phase III data from the DESTINY-Breast03 trial, progression-free survival increased significantly enough to be considered for standard of care in the second line setting.
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3. Results of the KEYNOTE-355 trial found that patients with a PD-L1 expression score of 10 or higher would benefit from pembrolizumab in combination with chemotherapy. Overall survival and progression-free survival increased significantly and patients with triple negative metastatic breast cancer and PD-L1 expression saw a 27% reduction in risk of death
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4. Patients with HER2 positive metastatic breast cancer show improved survival receiving pyrotinib in combination with capecitabine compared to those receiving lapatinib plus capecitabine. In phase III results of the PHOEBE trial, patients who progressed on trastuzumab and pertuzumab plus chemotherapy showed a 31% lower risk of death and had longer progression-free survival when treated with pyrotinib plus capecitabine.
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5. New data suggests that genomic profiling can improve outcomes for patients with metastatic breast cancer. Combined analysis of two trials found that progression-free survival increased when treatment was targeted based on genomic testing including patients with PIK3CA-mutated breast cancer.
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