What adjuvant therapy is recommended for a HER2‑negative (human epidermal growth factor receptor 2‑negative) breast cancer?

Adjuvant Therapy for HER2-Negative Breast Cancer

For HER2-negative breast cancer, adjuvant therapy is determined primarily by hormone receptor (HR) status, with HR-positive disease requiring endocrine therapy as the cornerstone and HR-negative (triple-negative) disease requiring chemotherapy-based approaches, with additional targeted agents added based on specific high-risk features. 1

HR-Positive/HER2-Negative Disease

Standard Risk Disease

• Adjuvant endocrine therapy is category 1 recommendation for all HR-positive/HER2-negative breast cancer regardless of stage. 1

• For node-negative disease with low-risk features, endocrine therapy alone may be sufficient, with genomic assays (Oncotype DX, MammaPrint, Breast Cancer Index, EndoPredict) used to guide chemotherapy decisions in postmenopausal patients or those >50 years. 2

• For 1-3 positive nodes, genomic assays can guide chemotherapy decisions in postmenopausal patients, though premenopausal patients with 1-3 positive nodes generally benefit from chemotherapy regardless of genomic assay results. 2

High-Risk Disease Requiring Intensified Therapy

For patients with ≥4 positive lymph nodes or high-risk residual disease after neoadjuvant therapy (CPS+EG score ≥3), add targeted agents to endocrine therapy: 1

• Abemaciclib (CDK4/6 inhibitor) for 2 years in select high-risk patients with node-positive disease after adjuvant chemotherapy. 1, 3

• Olaparib (PARP inhibitor) for 1 year in patients with germline BRCA1/2 mutations and ≥4 positive nodes after adjuvant chemotherapy or residual disease after neoadjuvant therapy with CPS+EG score ≥3. 1

  • Olaparib should be given concomitantly with endocrine therapy. 1
  • If both olaparib and abemaciclib are indicated, give olaparib first due to overlapping toxicities; do not combine. 1

Additional Considerations

• Adjuvant bisphosphonate therapy should be considered for 3-5 years in postmenopausal patients (natural or induced) with high-risk node-negative or node-positive tumors to reduce distant metastasis risk. 1

• Ovarian suppression/ablation should be added to endocrine therapy in premenopausal patients with ≥4 positive nodes (pN2/pN3). 1

HR-Negative/HER2-Negative Disease (Triple-Negative)

Neoadjuvant Setting (Preferred for Stage II-III)

• Chemotherapy plus pembrolizumab is recommended for cT1c-4 N0 or any N-positive disease (stage II-III), unless contraindications to immune checkpoint inhibitors exist. 1
  • Pembrolizumab is given every 3 weeks throughout neoadjuvant phase and continued for nine additional 3-week cycles in the adjuvant phase. 1

Adjuvant Setting After Surgery or Neoadjuvant Therapy

For residual disease after neoadjuvant therapy or high-risk features after primary surgery: 1

• Continue pembrolizumab if pembrolizumab-containing regimen was given preoperatively. 1

• Adjuvant capecitabine (6-8 cycles) for residual disease after neoadjuvant chemotherapy. 1

• Adjuvant olaparib for 1 year if germline BRCA1/2 mutation is present (category 1). 1

Low-Risk Exceptions

• Very low clinical risk tumors (pT1a pN0) or special histological subtypes (secretory, adenoid cystic carcinomas) may not require chemotherapy. 1

Critical Caveats

• ER-low positive tumors (1-9% ER expression) are heterogeneous and may behave more like triple-negative disease; individualize treatment considering both chemotherapy and endocrine therapy with careful risk-benefit assessment. 1

• Chemotherapy duration should be 12-24 weeks (4-8 cycles) depending on stage and regimen, with dose-dense schedules preferred when using anthracycline-based regimens. 1

• No genomic assays are validated for treatment guidance in patients with ≥4 positive nodes or in triple-negative breast cancer. 2