Management of Triple-Negative Breast Cancer (TNBC)

Overview

Staging-Based Approach

Stage I TNBC (Small, Node-Negative Tumors)

• Tumors < 5 mm (T1aN0) - may safely omit neoadjuvant chemotherapy; upfront surgery is appropriate per NCCN and ESMO guidelines.
• Tumors 5-10 mm (T1b/c), node-negative - upfront surgery is preferred to establish pathologic stage, which helps refine chemotherapy selection.
• Adjuvant chemotherapy with an anthracycline + taxane-based regimen is standard for higher-risk stage I disease.
• Neoadjuvant immunotherapy (pembrolizumab) is generally not recommended for low-risk stage I disease; the benefit-risk ratio favors omission.

Stage II-III TNBC (Locally Advanced)

Neoadjuvant Chemotherapy Backbone

• Anthracycline + cyclophosphamide (AC) x 4 cycles, followed by
• Taxane (paclitaxel or nab-paclitaxel) + carboplatin x 4 cycles

Adding Immunotherapy: KEYNOTE-522

• Significant improvement in pCR rates and event-free survival (EFS) with pembrolizumab added to chemotherapy.
• FDA approved for this indication.
• Notably, benefit was seen in both PD-L1-positive and PD-L1-negative tumors - therefore PD-L1 testing is not required before starting neoadjuvant pembrolizumab.
• Pembrolizumab is continued adjuvantly to complete 1 year total.
• Important caveat: ~40% of patients achieve pCR with chemotherapy alone, so ICI addition is not universally mandated in all operable TNBC cases.

Post-Neoadjuvant Therapy (Based on Response)

Targeted Therapy: PARP Inhibitors

• Metastatic setting: Both olaparib (OlympiAD trial) and talazoparib (EMBRACA trial) showed significant improvement in median PFS vs. physician's choice chemotherapy in germline BRCA1/2-mutated, HER2-negative metastatic breast cancer. FDA approved.
  • Olaparib: higher incidence of nausea
  • Talazoparib: higher incidence of cytopenias and alopecia
• Adjuvant setting: OlympiA trial - 1 year of adjuvant olaparib in high-risk germline BRCA1/2-mutated patients (post-neoadjuvant or adjuvant chemo) significantly reduced 3-year DFS events. Now FDA approved for this indication.
• Ongoing studies are evaluating PARP inhibition in patients with other DNA damage response pathway defects beyond germline BRCA1/2 mutations.

Metastatic TNBC (mTNBC) Management

First-Line Therapy

Second-Line and Beyond

Note on ADC sequencing: Four ADCs are now approved/emerging for TNBC. Research shows the second ADC used tends to be less effective, making the sequence of ADC selection clinically important. The optimal sequencing strategy remains under active investigation.

Immune Checkpoint Inhibitors: Key Principles

• Tumor-infiltrating lymphocyte (TIL) density is higher in TNBC vs. HR+ disease, supporting immunogenicity.
• ICI monotherapy showed only modest benefit; combination with chemotherapy substantially improves outcomes by causing neoantigen release.
• Immune-related adverse events (irAEs) to monitor: skin rash, thyroid dysfunction, inflammatory arthritis, colitis, pneumonitis, hypophysitis.
• PD-L1 testing (using CPS scoring) is required before first-line pembrolizumab in metastatic disease (KEYNOTE-355), but not required for neoadjuvant pembrolizumab (KEYNOTE-522).

Surgical Considerations

• Breast-conserving surgery (lumpectomy) is appropriate if NAC achieves adequate downstaging; margins of "no tumor at inked surface" are the standard.
• Mastectomy is indicated when BCS is contraindicated, for inflammatory breast cancer, or by patient preference.
• Axillary management: NAC can downstage axillary nodal disease, allowing targeted sentinel node dissection (clipped node + 2-3 sentinel nodes) rather than full axillary dissection - reducing lymphedema risk.
• Oncoplastic techniques should be considered when resection volume would otherwise yield an unacceptable cosmetic outcome.

Radiation Therapy

• Adjuvant radiotherapy is standard after BCS.
• Post-mastectomy radiotherapy (PMRT) is indicated in node-positive disease or large primary tumors per standard guidelines.

Biomarker Testing Recommended in TNBC

Summary Algorithm

TNBC Diagnosis
│
├── Early-Stage (Stage I-III)
│   ├── T1a, node-negative → Upfront surgery, then adjuvant chemo
│   ├── ≥T1c node+ or ≥T2 → Neoadjuvant chemo ± pembrolizumab (KEYNOTE-522)
│   │   ├── pCR → Complete adjuvant pembrolizumab (if used)
│   │   └── Residual disease → Capecitabine ± olaparib (if gBRCA+)
│   └── gBRCA1/2+ & high-risk → Adjuvant olaparib (OlympiA)
│
└── Metastatic (Stage IV)
    ├── PD-L1+ (CPS ≥10) → Pembrolizumab + chemo (KEYNOTE-355)
    ├── PD-L1- → Chemo alone (or Dato-DXd, emerging)
    ├── 2nd line → Sacituzumab govitecan (ASCENT)
    ├── gBRCA1/2+ → Olaparib / talazoparib
    ├── HER2-low → T-DXd (DESTINY-Breast04)
    └── MSI-H/TMB-high/NTRK/RET → Matched targeted therapy