The Breast - Anatomy, ANDI, Carcinoma, and Management

1. ANATOMY AND PHYSIOLOGY

• Arterial: Internal mammary artery (medial), lateral thoracic and acromiothoracic branches of the axillary artery (lateral), and intercostal perforators.
• Venous drainage: Axillary vein, internal thoracic vein, and intercostal veins.

• ~75% drains to axillary nodes (anterior/pectoral, central, posterior/subscapular, lateral, apical/infraclavicular)
• ~25% drains to internal mammary nodes (especially from medial and central breast)
• The sentinel node is the first draining node and is the basis for sentinel lymph node biopsy (SLNB)

• Thelarche (onset at puberty)
• Pregnancy-induced proliferation under estrogen and progesterone
• Involution after menopause (replaced by fat)

2. ANDI - ABERRATIONS OF NORMAL DEVELOPMENT AND INVOLUTION

ANDI Classification Table

Key ANDI entities explained:

Cancer risk associated with benign breast conditions:

3. BREAST CARCINOMA

3.1 Epidemiology

3.2 Risk Factors

• Obesity (BMI >30): RR 1.29 (postmenopausal)
• Nulliparity or first pregnancy >35 years
• HRT use >10 years: RR 1.2
• Alcohol: RR 1.05 (light) to 1.46 (heavy >4 drinks/day)
• Smoking: RR 1.14 (>25 cigarettes/day)
• Radiation exposure: RR 6
• Late menopause, early menarche (increased lifetime estrogen exposure)

• Age - most important risk factor
• Female sex
• Family history / BRCA mutations
• Dense breast tissue
• Prior benign breast disease with atypia

3.3 Genetic Basis

• ~12% of all breast cancers are caused by germline mutations
• BRCA1 (chromosome 17q21): 50-85% lifetime risk of breast cancer; up to 40% risk of ovarian cancer; associated cancers are mostly triple negative (ER-/PR-/HER2-)
• BRCA2 (chromosome 13q12.3): 50-60% lifetime risk of breast cancer; 20% ovarian cancer risk; also associated with prostate, colon, pancreatic, and gallbladder cancer
• Other hereditary syndromes: Li-Fraumeni (TP53), Cowden syndrome (PTEN), Peutz-Jeghers, hereditary gastric cancer syndrome

3.4 Molecular Subtypes (Intrinsic Subtypes)

3.5 Pathological Classification

• DCIS (Ductal Carcinoma in Situ): Pre-invasive; confined to ducts. Most common presentation is mammographic microcalcifications. Subtypes: comedo (central necrosis - high grade), cribriform, micropapillary, solid. Comedo DCIS has the highest risk of progression. DCIS is a direct precursor to invasive ductal carcinoma in the same breast.
• LCIS (Lobular Carcinoma in Situ): A marker of increased risk (10x), not truly a pre-invasive lesion. When subsequent carcinoma occurs: 2/3 in same breast, 1/3 in contralateral breast. Managed with close surveillance or chemoprevention.

1. Invasive Ductal Carcinoma (IDC) of No Special Type (NST) - 80% of all invasive breast cancers. Hard, irregular mass; chalky-white stellate cut surface (scirrhous). Desmoplastic stromal reaction. 75% are ER-positive. Prognosis depends on grade and nodal status.
2. Invasive Lobular Carcinoma (ILC) - 10-15%. Single-file "Indian file" pattern of cells; no E-cadherin expression. More likely to be bilateral and multicentric. Notoriously difficult to detect on mammogram.
3. Medullary Carcinoma - 4%. Soft, hemorrhagic, bulky. Microscopically: dense lymphoreticular infiltrate, large pleomorphic nuclei, sheet-like growth. Frequently BRCA1-associated. <10% ER-positive. Better prognosis than NST despite high grade. (Note: now classified as IDC-NST with "medullary pattern" in current WHO classification)
4. Mucinous (Colloid) Carcinoma - 2%. Older patients. Extracellular mucin pools surrounding low-grade cells. >90% ER-positive. 5-year survival ~73%; favorable prognosis.
5. Tubular Carcinoma - 2%. Well-differentiated angulated tubules with open lumina; single epithelial cell layer. Excellent prognosis.
6. Papillary Carcinoma - 2%. 7th decade; fibrovascular stalks with multilayered epithelium. Rarely >3 cm.
7. Paget's Disease of the Nipple - Chronic eczematous eruption of nipple, associated with underlying DCIS/invasive cancer. Pathognomonic: Paget cells (large, pale, vacuolated cells in rete pegs). Immunostaining: CEA-positive (vs S-100 in melanoma). Treatment: lumpectomy or mastectomy depending on extent.
8. Inflammatory Breast Carcinoma - Worst prognosis. Erythema and peau d'orange involving >1/3 of breast skin due to dermal lymphatic invasion. Does NOT require a palpable mass. Treatment: neoadjuvant chemotherapy followed by modified radical mastectomy (NOT breast-conserving surgery).

3.6 Histological Grading (Nottingham/Bloom-Richardson-Elston)

• Grade 1 (3-5): Well differentiated - tubule formation >75%; small, uniform nuclei; <2 mitoses/HPF
• Grade 2 (6-7): Moderately differentiated
• Grade 3 (8-9): Poorly differentiated - solid sheets; irregular nuclei; >2 mitoses/HPF; necrosis

3.7 Clinical Presentation

• Lump in the breast (most common): hard, irregular, non-tender, ill-defined margins, skin/nipple tethering
• Nipple discharge (blood-stained)
• Nipple retraction (new-onset)
• Peau d'orange (lymphatic obstruction)
• Skin ulceration or chest wall fixity (locally advanced)
• Cancer en cuirasse: extensive skin infiltration
• Mondor's disease: thrombophlebitis of superficial thoracoepigastric veins, appearing as a cord-like lesion on the lateral breast

4. INVESTIGATIONS AND STAGING

4.1 Triple Assessment

1. Clinical examination - history + physical exam
2. Imaging - mammogram (women >35 years) ± ultrasound (all ages for solid/cystic differentiation)
3. Pathology - core needle biopsy (preferred) or fine needle aspiration cytology (FNAC)

4.2 Imaging

4.3 Staging - AJCC 8th Edition TNM

5. MANAGEMENT

5.1 Surgical Management

• Removal of tumor with adequate margins
• Oncologically equivalent to mastectomy for early disease (multiple RCTs; NSABP B-06)
• Mandatory radiotherapy after BCS to the remaining breast
• Contraindicated in: multicentric disease, diffuse DCIS, pregnancy (1st/2nd trimester), prior breast irradiation, connective tissue disorder, inability to achieve clear margins

• Removes entire breast including NAC + axillary contents (levels I-III); preserves pectoralis muscles (Patey's modification)
• Indications: large tumor/small breast, multicentric disease, BRCA-positive, patient preference, local recurrence after BCS, inflammatory carcinoma
• Radical mastectomy (Halsted) - historically used but now rarely indicated due to excessive morbidity (winged scapula, lymphedema, shoulder dysfunction) with no survival benefit

• SLNB (Sentinel Lymph Node Biopsy): Standard of care for clinically node-negative axilla. Uses blue dye ± radioisotope (Tc-99m sulphur colloid). If sentinel node negative - axillary dissection is avoided. False-negative rate must be <10%.
• Axillary Node Dissection (ALND): For clinically or SLNB-positive axilla.
• Axillary Reverse Mapping: Technique to identify and preserve arm lymphatics during ALND to reduce lymphedema.

• Neoadjuvant chemotherapy (NACT) first, then surgery (mastectomy or BCS if good response)
• Inflammatory carcinoma - NACT then MRM (BCS contraindicated)

• Immediate or delayed
• Implant-based (tissue expander + silicone, subpectoral)
• Autologous flaps:
  • LD flap (Latissimus dorsi) - pedicled
  • TRAM flap (Transverse Rectus Abdominis Myocutaneous) - pedicled or free
  • DIEP flap (Deep Inferior Epigastric Perforator) - most commonly used in the UK; requires microvascular skills; ~4 hours operative time
  • Anterolateral thigh (ALT) free flap

5.2 Radiotherapy

• Always after BCS (breast/chest wall + regional nodes if node-positive)
• Post-mastectomy RT (PMRT) if: tumor ≥5 cm, skin/chest wall involvement, lymphovascular invasion (LVI), grade 3, axillary LN positive

• Standard: 45-50.4 Gy in 25 fractions
• Hypofractionation: 40-42.5 Gy in 15-16 fractions (increasingly standard)
• Boost to tumor bed: additional 10-16 Gy reduces local recurrence

5.3 Adjuvant Systemic Therapy

• CMF (cyclophosphamide, methotrexate, 5-FU) - older regimen
• Anthracycline-based: CAF/CEF, AC
• Taxane-based: docetaxel, paclitaxel
• Standard modern regimens: AC-T (anthracycline-cyclophosphamide followed by taxane); TC; carboplatin added for aggressive biology/BRCA-mutated TNBC

• Oncotype DX (21-gene recurrence score): RS <18 = low risk (endocrine therapy alone); RS 19-30 = intermediate; RS >30 = high (benefit from chemo). TAILORx trial validated: RS 0-10 has 98.7% disease-free survival at 5 years with endocrine therapy alone.
• MammaPrint (70-gene): FDA approved; MINDACT trial showed low-genomic-risk patients with high clinical risk can avoid chemotherapy (92% distant metastasis-free survival at 5 years)
• Prosigna (PAM50): Provides risk of recurrence score

• Tamoxifen: SERM; used in premenopausal women; 5 years standard (10 years in high-risk: node+, tumor >5 cm, LVI)
• Aromatase Inhibitors (AIs): Anastrozole, letrozole, exemestane; postmenopausal women; superior to tamoxifen for relapse-free and overall survival but associated with bone density loss and fracture risk (bisphosphonates +/- calcium/vitamin D required)
• Pre/perimenopausal women requiring ovarian suppression + AI: GnRH agonists (goserelin) used

• Trastuzumab (Herceptin): Monoclonal antibody against HER2 extracellular domain; 1 year adjuvant therapy with chemotherapy; reduces recurrence by ~50%
• Pertuzumab: Anti-HER2 antibody targeting dimerization domain; combined with trastuzumab + taxane (neoadjuvant and adjuvant for high-risk HER2+)
• T-DM1 (ado-trastuzumab emtansine): Antibody-drug conjugate; standard of care for residual invasive disease after neoadjuvant therapy for HER2+ cancer (KATHERINE trial)
• Neratinib: Extended adjuvant after trastuzumab (ExteNET trial); hormone receptor-positive HER2+ patients

• Palbociclib, Ribociclib, Abemaciclib - inhibit cyclin D1-CDK4/6 complex, preventing G1-S transition
• Standard of care in HR+/HER2- metastatic breast cancer (combined with aromatase inhibitor or fulvestrant)
• Abemaciclib now approved in adjuvant setting for high-risk HR+/HER2- early breast cancer (monarchE trial): significantly improves invasive disease-free survival
• A 2025 meta-analysis (PMID 39656361) confirmed efficacy and safety of CDK4/6 inhibitors across randomized controlled trials and real-world settings
• REIGNITE systematic review (2025, PMID 41037898): evidence for continuing CDK4/6 inhibitors beyond progression

• Olaparib, Talazoparib: PARP inhibitors exploit synthetic lethality in BRCA1/2-mutated tumors
• Olaparib approved for adjuvant treatment of germline BRCA-mutated, HER2-negative early breast cancer after chemotherapy (OlympiA trial: improved iDFS and overall survival)
• Talazoparib for germline BRCA-mutated metastatic HER2- breast cancer

• Pembrolizumab (anti-PD-1): Approved in combination with chemotherapy for early TNBC (neoadjuvant + adjuvant) based on KEYNOTE-522 trial - significantly improves pCR rate and event-free survival
• Pembrolizumab also approved for metastatic PD-L1-positive TNBC (KEYNOTE-355)
• Atezolizumab (anti-PD-L1): Previously approved for first-line metastatic TNBC (IMpassion130) but FDA approval withdrawn; pembrolizumab now the standard
• A systematic review of targeted treatment in metastatic TNBC (PMID 39742383) confirms immunotherapy + chemotherapy as the backbone for PD-L1+ TNBC
• Immune checkpoint inhibitor combinations are being refined; a 2026 meta-analysis (PMID 41632000) characterized immune-related adverse events with these regimens

• Alpelisib: PI3K-alpha inhibitor; approved with fulvestrant for HR+/HER2-, PIK3CA-mutated metastatic breast cancer post-CDK4/6 inhibitor failure
• PIK3CA mutations (~40% of HR+ breast cancers) detectable by circulating tumor DNA (liquid biopsy)

• Sacituzumab govitecan (SG): Anti-TROP-2 ADC; approved for metastatic TNBC and HR+/HER2- metastatic breast cancer
• Trastuzumab deruxtecan (T-DXd): Anti-HER2 ADC; approved for HER2-low (IHC 1+ or 2+/FISH-) metastatic breast cancer (DESTINY-Breast04 trial) - a major paradigm shift; and for HER2+ metastatic breast cancer
• Precision breast oncology with these agents is covered in a 2026 systematic review (PMID 42134177)

5.4 Management by Subtype Summary

5.5 Metastatic / Stage IV Disease

• HR+ / bone-limited metastases: Endocrine therapy first-line (+ CDK4/6 inhibitor)
• HR- or visceral crisis: Systemic chemotherapy first
• Bone metastases: Bisphosphonates (zoledronic acid) or denosumab; palliative RT to weight-bearing sites
• Pleural effusion: Chest drain + pleurodesis
• Metronomic chemotherapy: Low-dose oral cyclophosphamide/capecitabine; cytostatic and antiangiogenic

5.6 Follow-up after Treatment

• Clinical examination every 3 months x 2 years, then every 6 months x 3 years, then yearly
• Annual mammography
• Annual MRI for BRCA carriers or implant patients
• Bone densitometry before starting aromatase inhibitors

6. HEREDITARY BREAST CANCER AND PROPHYLAXIS

• BRCA1/2 carriers: Risk-reducing mastectomy (reduces risk by ~90%) and salpingo-oophorectomy (reduces ovarian cancer risk and lowers breast cancer risk by reducing estrogen)
• Chemoprevention: Tamoxifen (premenopausal), raloxifene or AIs (postmenopausal) reduce risk in high-risk women by 30-40%
• Genetic testing indications: early-onset (<40 years), bilateral disease, male breast cancer, family clustering, TNBC histology

7. RECENT ADVANCES (2024-2026 Highlights)

• Schwartz's Principles of Surgery, 11th Edition (ANDI classification, benign breast disorders, surgical management)
• Bailey and Love's Short Practice of Surgery, 28th Edition (epidemiology, staging, systemic therapy)
• Robbins, Cotran & Kumar Pathologic Basis of Disease (molecular subtypes, staging, management overview)
• Robbins & Kumar Basic Pathology (breast carcinoma subtypes)
• Sabiston Textbook of Surgery (anatomy, surgical therapy, axillary management, genomic assays)
• Recent meta-analyses: CDK4/6 inhibitors [PMID 39656361], TNBC targeted therapy [PMID 39742383], precision breast oncology [PMID 42134177], immune checkpoint combinations [PMID 41632000]