Breast Cancer
Breast Carcinoma · Mammary Cancer
Most common cancer in women worldwide — ~2.3 million new cases/year
Breast cancer is not one disease but a collection of distinct molecular subtypes with different prognoses and treatment strategies. The four main intrinsic subtypes — determined by ER, PR, HER2, and Ki67 — dictate treatment. Genetic testing (BRCA1/2, PALB2) is critical for surgical and systemic treatment decisions. Genomic assays (Oncotype DX, MammaPrint) help determine which early-stage hormone receptor-positive patients need chemotherapy.
5
Subtypes
12
Diagnostic Tests
16
Treatment Options
For Informational Purposes Only
Content on this page is for educational purposes only and does not constitute medical advice.
🗺 What Do I Do Next? — Your Roadmap
Just diagnosed with Breast Cancer? Here are your essential next steps.
Get the Full Diagnostic Workup
Before any treatment begins, you need 12 key tests — imaging, blood markers, biopsy, and molecular profiling. See the Diagnostic Workup section below. Do NOT start treatment without molecular testing — it determines which therapies work for your specific subtype.
Know Your Molecular Subtype
Breast Cancer is not one disease — it has 5 distinct subtypes defined by biomarkers (ER, PR, HER2, Ki67, and more). Your subtype determines which treatments apply to you. See Subtypes & Mutations below.
Assemble Your Care Team
You need a multidisciplinary team: oncologist (medical, surgical, radiation), pathologist, radiologist, and ideally a molecular tumour board review. Seek a second opinion at a major cancer centre for any Stage III-IV diagnosis.
Review All Treatment Options
Treatment for Breast Cancer spans Surgery, Chemotherapy, Radiation, Targeted Therapy, Immunotherapy, Hormonal. See the full Treatment Options section below. Ask your oncologist which options apply to your specific subtype and stage.
Ask About Clinical Trials
Many of the most effective treatments started as clinical trials. Ask your oncologist about eligibility. Search clinicaltrials.gov with your cancer type + molecular profile. Academic centres have the most trials.
Key Biomarkers & Mutations
Subtypes & Molecular Profiles
Slowest-growing, best-prognosis subtype. Responds well to endocrine therapy alone. Chemotherapy adds little benefit. Oncotype DX score < 11 identifies patients who can safely omit chemotherapy even with node-positive disease (RxPONDER trial).
KEY THERAPIES FOR THIS SUBTYPE
Diagnostic Workup
12 testsBIOPSY & PATHOLOGY
Core Needle Biopsy of Breast Mass
At diagnosisObtain tissue for histology (invasive vs. in-situ), grade, ER/PR/HER2/Ki67 — essential for subtype classification.
ER / PR / HER2 / Ki67 Immunohistochemistry
On biopsy specimenDefines breast cancer subtype. HER2 equivocal (IHC 2+) requires FISH/ISH. Ki67 guides chemotherapy decision.
IMAGING
Mammography + Ultrasound
At diagnosisAssess size, multicentricity, axillary lymph nodes. Bilateral imaging mandatory.
Breast MRI
At diagnosis, especially pre-neoadjuvantExtent of disease — multifocal/multicentric disease, contralateral breast, pectoralis involvement. Mandatory before neoadjuvant therapy.
CT Chest / Abdomen / Pelvis
Stage III-IV or high-risk Stage IIStaging for distant metastases — lung, liver, bone, adrenal. Required for Stage III-IV and symptomatic patients.
Bone Scan or PET-CT
Stage III-IV, bone pain, elevated ALPDetect bone metastases (most common metastatic site in HR+ breast cancer). PET-CT more sensitive.
ENDOSCOPY & PROCEDURE
Sentinel Lymph Node Biopsy (SLNB)
At surgeryAssess axillary node involvement — avoids full axillary clearance if SLNB negative. Key for surgical staging.
GENETIC & MOLECULAR
Oncotype DX (21-gene assay)
Early-stage HR+/HER2- after surgeryPredicts chemotherapy benefit in Stage I-III, HR+/HER2-, node-negative or 1-3 node-positive disease. Recurrence score 0–100.
MammaPrint (70-gene signature)
Early-stage HR+/HER2-, clinical high riskClassifies tumour as low or high genomic risk. MINDACT trial: low genomic risk patients can safely omit chemotherapy.
Germline BRCA1/2 / PALB2 Testing
All triple-negative, age < 50, strong family history, bilateral cancerBRCA1/2 and PALB2 germline mutation guides surgical decision, PARP inhibitor eligibility, and family testing.
Tumour Genomic Profiling (ctDNA / tissue)
Metastatic setting or refractory diseasePIK3CA mutation (everolimus/alpelisib eligibility in HR+ metastatic), PD-L1 (pembrolizumab in TNBC), ESR1 (endocrine resistance). Foundation One / Guardant.
BLOOD & TUMOUR MARKERS
Bone Density Scan (DEXA)
Before starting aromatase inhibitorBaseline before aromatase inhibitor therapy — AI therapy causes bone loss, bisphosphonate often co-prescribed.
Treatment Options
16 optionsSURGERY
Breast-Conserving Surgery (Lumpectomy + Radiation)
Standard for early-stage (T1-2, N0-1) breast cancer. Equivalent survival to mastectomy when followed by radiation. Preferred approach when feasible.
Mastectomy (Total / Modified Radical)
Larger tumours, multifocal disease, inflammatory breast cancer, BRCA carriers, patient preference. Immediate reconstruction offered.
Axillary Lymph Node Dissection (ALND)
4+ positive nodes, node-positive disease after neoadjuvant chemotherapy with residual disease.
CHEMOTHERAPY
AC-T (Doxorubicin + Cyclophosphamide → Paclitaxel)
Standard curative chemotherapy for early-stage breast cancer. Dense-dose AC every 2 weeks → weekly paclitaxel. Node-positive HR+ and most TNBC.
TC (Docetaxel + Cyclophosphamide)
Node-negative early-stage breast cancer — avoids anthracycline cardiotoxicity. Non-inferior to AC in low-risk patients.
TCHP (Docetaxel + Carboplatin + Trastuzumab + Pertuzumab)
HER2+ early-stage — standard neoadjuvant or adjuvant. pCR rates 40–60%. Avoids anthracycline.
RADIATION
Whole Breast Radiation (WBI / APBI)
After lumpectomy — standard of care reduces local recurrence by ~70%. Accelerated partial breast irradiation (APBI) for low-risk early-stage.
Post-Mastectomy Radiation (PMRT)
After mastectomy with ≥4 positive nodes, T3-4 tumour, or positive margins.
TARGETED THERAPY
CDK4/6 Inhibitors (Palbociclib / Ribociclib / Abemaciclib)
HR+/HER2- metastatic breast cancer — added to AI doubles PFS (PALOMA, MONALEESA, MONARCH trials). Abemaciclib also approved adjuvant (MonarchE — high-risk node-positive).
T-DM1 / Ado-Trastuzumab Emtansine (Kadcyla)
HER2+ residual disease after neoadjuvant TCHP — KATHERINE trial: 50% reduction in recurrence vs trastuzumab. Also second-line metastatic HER2+.
T-DXd / Trastuzumab Deruxtecan (Enhertu)
HER2+ metastatic (second-line) — DESTINY-Breast03: superior to T-DM1. Also active in HER2-low (IHC 1+/2+ FISH-negative) — new indication.
Olaparib / Talazoparib (PARP Inhibitors)
Germline BRCA1/2-mutant HER2-negative metastatic breast cancer. Superior to chemotherapy (OlympiAD, EMBRACA trials).
Sacituzumab Govitecan (Trodelvy)
Previously treated metastatic TNBC (≥2 prior lines). Also HR+/HER2- after endocrine therapy. Antibody-drug conjugate targeting TROP-2.
IMMUNOTHERAPY
Pembrolizumab + Chemotherapy (KEYNOTE-522)
High-risk early TNBC (Stage II-III) — neoadjuvant then adjuvant pembrolizumab. FDA-approved. Increases pCR from 51% → 65%.
HORMONAL
Tamoxifen
ER+ pre- and postmenopausal patients. 5–10 years adjuvant therapy. Reduces recurrence by ~40%. First-line metastatic HR+ if not previously used.
Aromatase Inhibitors (Letrozole / Anastrozole / Exemestane)
Postmenopausal ER+ — superior to tamoxifen for distant recurrence. 5–10 years adjuvant. Standard metastatic HR+ first-line (with CDK4/6 inhibitor).