SABCS 2020: update on triple-negative and metastatic HER2-positive breast cancer

One year into the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) pandemic, the 2020 San Antonio Breast Cancer Symposium (SABCS) was another large congress held in a virtual format. Despite these circumstances, clinically relevant data were presented, and this short review focuses on developments in the fields of triple-negative breast cancer (TNBC) and metastatic HER2-positive breast cancer. A quality-of-life (QoL) analysis from IMPassion031 showed that adding atezolizumab to neoadjuvant chemotherapy was not associated with a detrimental effect on QoL, while the burden of treatment-induced side effects increased with each cycle of neoadjuvant therapy in both treatment arms. KEYNOTE-355 evaluated the addition of pembrolizumab to chemotherapy as first-line treatment in metastatic TNBC (mTNBC); a significant improvement of progression-free survival (PFS) was reported in the pembrolizumab arm. At the 2020 SABCS, results with respect to different chemotherapy backbones were reported and the benefit of pembrolizumab was maintained irrespective of the type of taxane. Disappointingly, the phase III IPATunity130 study could not confirm a PFS improvement with the AKT inhibitor ipatasertib when added to paclitaxel as first-line treatment in mTNBC. A biomarker analysis from the phase III ASCENT study showed that the antibody-drug conjugate sacituzumab govitecan was superior to chemotherapy by investigator's choice independent of Trop-2 expression and BRCA mutation status. In HER2-positive breast cancer, the PRECIOUS trial suggested a small albeit significant benefit with reinduction of pertuzumab in later treatment lines in patients progressing on prior dual HER2-blockade in the first- or second-line setting. The HER2-specific tyrosine kinase inhibitor tucatinib when added to trastuzumab and capecitabine was shown to improve PFS and overall survival (OS) over trastuzumab and capecitabine alone in pretreated patients in the randomized HER2CLIMB trial; this benefit was apparently independent of hormone-receptor expression. An update from the DESTINY-Breast01 trial reported a median PFS of 19.4 months with trastuzumab deruxtecan in heavily pretreated patients. Finally, an analysis from the PERTAIN trial with > 6 years median follow-up showed excellent OS in patients with luminal B/HER2-positive receiving first-line trastuzumab/pertuzumab in combination with endocrine therapy suggesting that chemotherapy-free treatment is an option in highly selected patients.