Definition A malignant tumor that starts in the epithelial lining of the breast’s milk ducts, breaks through the duct wall, and invades the surrounding breast tissue, with potential to metastasize to lymph nodes and distant organs.
Key Features for Oncology/Pharmacy Context
- Origin: Terminal ductal–lobular unit (TDLU).
- Histology: Irregular nests or cords of malignant epithelial cells infiltrating the stroma, often with desmoplastic reaction.
- Receptor Status: Can be ER/PR positive or negative, HER2 positive or negative — testing guides systemic therapy.
- Common Presentation:
- Palpable breast lump
- Skin dimpling or nipple retraction
- Possible bloody nipple discharge
- Diagnosis:
- Mammography ± ultrasound
- Core needle biopsy (histologic confirmation)
- Immunohistochemistry for ER, PR, HER2
- Treatment Overview:
- Local therapy: Surgery (lumpectomy or mastectomy) ± radiation
- Systemic therapy:
- Endocrine therapy if ER/PR+
- HER2-targeted therapy if HER2+
- Chemotherapy for high-risk or triple-negative disease
Prognosis Factors
- Tumor size and grade
- Lymph node involvement
- Hormone receptor and HER2 status
- Ki-67 proliferation index
| Subtype | Key Biomarkers | Typical Staging at Dx | First-Line Systemic Therapy | Key Notes / Pharmacist Considerations |
|---|---|---|---|---|
| Hormone receptor–positive / HER2-negative | ER+, PR+, HER2– | Early (I–III) or metastatic | Early stage: Surgery ± radiation → adjuvant endocrine therapy (tamoxifen or aromatase inhibitor ± CDK4/6 inhibitor in high-risk) Metastatic: Endocrine therapy + CDK4/6 inhibitor (palbociclib, ribociclib, abemaciclib) |
Monitor for endocrine therapy side effects (VTE, menopausal symptoms, bone density). CDK4/6 inhibitors → CBC monitoring for neutropenia. |
| HER2-positive (any HR status) | HER2 overexpression/amplification (IHC 3+ or FISH+) | Early (I–III) or metastatic | Early stage: Surgery ± radiation → trastuzumab-based regimen (TCHP or AC-THP). Metastatic: Trastuzumab + pertuzumab + taxane (THP) first-line |
Monitor cardiac function (LVEF) for HER2-targeted agents; taxanes → neuropathy risk. |
| Triple-negative (ER–, PR–, HER2–) | All three negative | Often higher grade; may be aggressive | Early stage: Neoadjuvant chemo (anthracycline + taxane ± carboplatin). Metastatic: Chemo ± immunotherapy if PD-L1+ (atezolizumab + nab-paclitaxel or pembrolizumab + chemo) |
High recurrence risk; immune-related adverse effects with checkpoint inhibitors; manage chemo toxicities aggressively. |
| Inflammatory breast cancer (any subtype) | Variable | Usually stage III | Neoadjuvant systemic therapy based on receptor status → surgery → radiation | Aggressive disease; tight coordination with oncology team for sequence of therapy. |