Breast
Benign disease, in-situ vs invasive carcinoma, the axilla, and special presentations for the Surgery Shelf.
Sources: TPOT-Surgery_Endocrine_GI.pdf (Breast, pp.89–100); First Aid 2026 (first-aid-usmle-bible).
High-Yield Points
- Biggest risk factors are female sex and age; then first-degree family history, prior DCIS/LCIS, and lifetime estrogen exposure (early menarche, late menopause, nulliparity, obesity). BRCA1/2 = high lifetime breast/ovarian risk (BRCA1 skews triple-negative) → MRI + mammography surveillance and option of risk-reducing mastectomy/salpingo-oophorectomy.
- Any palpable mass → triple assessment: clinical exam + imaging (mammography ± US) + needle biopsy (core preferred for histology/receptors). A solid or non-resolving mass needs tissue; discordance → excisional biopsy.
- DCIS: malignant ductal cells confined by basement membrane; comedo type shows central necrosis → microcalcifications. Rarely nodal → no routine axillary dissection; Tx lumpectomy + radiation (or simple mastectomy).
- LCIS: a marker of increased BILATERAL risk (not a local precursor) → surveillance, tamoxifen, or risk-reducing bilateral mastectomy.
- Invasive ductal carcinoma (NOS) = most common (~50–70%); desmoplastic → hard, fixed, skin-dimpling mass. Invasive lobular (~10–15%): single-file cells, E-cadherin loss, often bilateral/multifocal and mammographically subtle.
- Sentinel lymph node biopsy: negative → spare the axilla; positive → completion dissection (levels I–II) or axillary radiation.
- Adjuvant systemic therapy: ER/PR-positive → endocrine therapy (tamoxifen premenopausal; aromatase inhibitor postmenopausal). HER2-positive → trastuzumab. Post-mastectomy radiation for tumor >5 cm and/or ≥4 positive nodes.
Key Tables / Differentials
DCIS vs LCIS
| DCIS | LCIS | |
|---|---|---|
| Nature | Pre-malignant precursor (same breast) | Marker of bilateral risk |
| Imaging | Microcalcifications | Incidental, no calcifications |
| Management | Lumpectomy + RT / simple mastectomy | Surveillance, tamoxifen, ± risk-reducing mastectomy |
Invasive ductal vs lobular
| Ductal (NOS) | Lobular | |
|---|---|---|
| Frequency | Most common (50–70%) | 10–15% |
| Histology | Nests/cords, desmoplasia | Single-file, E-cadherin loss |
| Behavior | Discrete hard mass | Diffuse, often bilateral/multifocal |
Benign vs malignant axillary nerve injuries
| Nerve | Deficit |
|---|---|
| Long thoracic | Winged scapula (serratus anterior) |
| Thoracodorsal | Weak arm adduction/pull-ups (latissimus) |
| Intercostobrachial | Inner-arm numbness (often sacrificed) |
Board Pearls
- Rapidly enlarging red breast + peau d'orange not responding to antibiotics = inflammatory carcinoma (dermal lymphatic invasion) → biopsy, neoadjuvant chemo first.
- Chronic eczematous/scaling nipple lesion = Paget disease → biopsy; usually underlying carcinoma.
- Mobile, smooth, well-circumscribed lump in a young woman = fibroadenoma (most common benign tumor).
- Rapidly growing large multinodular mass, leaf-like stroma = phyllodes tumor → wide local excision (1–2 cm margins), no axillary dissection.
- Unilateral, single-duct, bloody discharge = intraductal papilloma; bilateral milky = galactorrhea (check prolactin).
- Lactational breast: tender wedge = mastitis (S. aureus) → antibiotics + keep emptying; fluctuant = abscess → drain.
Classic Vignette Triggers
- "Microcalcifications on screening, no mass, cells within duct" → DCIS.
- "Incidental small uniform cells in acini, no calcifications" → LCIS (marker of bilateral risk).
- "Single-file cells, loss of E-cadherin, vague thickening" → invasive lobular carcinoma.
- "Red, swollen, painful breast, peau d'orange, fails antibiotics" → inflammatory breast cancer.
- "Eczematous non-healing nipple" → Paget disease → biopsy.
- "22-year-old with a mobile, rubbery, painless lump" → fibroadenoma.
- "Winged scapula after axillary dissection" → long thoracic nerve injury.