HER2-Positive Tumor Cell
Gene amplification drives massive HER2 receptor overexpression on the surface.
- ~2.3M: HER2 receptors per cell (vs ~20K normal cells)
- 4–25×: HER2 gene copy number (amplified via ERBB2 gain)
- ~15–20%: HER2+ breast cancers (of all diagnoses)
- 1987: Discovery milestone (Slamon et al., Science)
Gene amplification
Extra ERBB2 gene copies drive receptor overproduction on the membrane.
Ligand-independent signaling
Dense receptors self-dimerize, firing growth signals without a ligand.
Clinical aggressiveness
HER2+ tumors historically grow faster and recur more often.
Trastuzumab Administered
A humanized monoclonal antibody is infused, engineered to bind HER2 precisely.
- 1998: FDA approval (first HER2-targeted therapy)
- IgG1: Antibody class (humanized monoclonal)
- ~28 days: Serum half-life (supports 3-week dosing)
- Domain IV: Binding target (HER2 extracellular region)
Engineered specificity
Fab arms are shaped to recognize only the HER2 extracellular domain.
Dosing regimen
Loading dose then maintenance infusions sustain steady blood levels.
Systemic distribution
Antibody circulates and diffuses toward HER2-rich tumor surfaces.
Receptor Blockade
Bound antibody physically prevents HER2 receptors from pairing and signaling.
- Yes: Dimerization blocked (domain IV occupancy)
- ↓ Suppressed: PI3K/AKT activity (downstream pathway)
- ↓ Suppressed: MAPK pathway (proliferation signal)
- Increased: Receptor internalization (reduces surface density)
Steric blockade
Bound antibody occupies the site needed for receptor pairing.
Pathway suppression
PI3K/AKT and MAPK growth cascades quiet down markedly.
Cell cycle arrest
Loss of growth signal slows tumor cell proliferation rate.
NK Cell ADCC Attack
Antibody-coated tumor cells are flagged for direct natural-killer cell destruction.
- FcγRIIIa (CD16): NK receptor (recognizes antibody Fc)
- ADCC: Mechanism (antibody-dependent cytotoxicity)
- Perforin/granzyme: Cytotoxic payload (released granules)
- Affects affinity: V158F polymorphism (response variability)
Fc recognition
NK cell CD16 receptors bind the antibody tail on the tumor.
Granule release
Perforin and granzyme punch and trigger tumor cell apoptosis.
Immune amplification
Multiple NK cells can engage a single flagged tumor cell.
Combined Blockade & Immune Killing
Growth-signal blockade plus ADCC together significantly shrink HER2+ tumor burden.
- ↑ Improved: Pathologic complete response (with trastuzumab regimens)
- + Pertuzumab: Combination therapy (dual HER2 blockade)
- T-DXd: Next-gen ADC (trastuzumab deruxtecan)
- Landmark: Survival benefit (biologic era milestone)
Dual mechanism benefit
Signal blockade and immune attack act together, not alone.
Combination regimens
Pairing with pertuzumab deepens the HER2 blockade further.
A biologic milestone
Trastuzumab remains a landmark receptor-targeted cancer therapy.