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Breast Cancer for USMLE Step 1

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Breast Cancer for the USMLE Step 1 Exam
Definition and Classification
  • Definition
    • Breast cancer is a malignant tumor originating in the breast tissue, primarily in the ducts (ductal carcinoma) or lobules (lobular carcinoma).
  • Classification by Receptor Status
    • Hormone Receptor-Positive (ER+ and/or PR+): Responsive to hormonal therapies, accounting for 70% of breast cancers.
    • HER2-Positive: Overexpression of HER2 receptor, associated with more aggressive behavior; targeted HER2 therapy is effective.
    • Triple-Negative Breast Cancer (TNBC): Lacks ER, PR, and HER2 expression; associated with a poorer prognosis and treated with chemotherapy.
Epidemiology
  • Incidence and Mortality
    • Breast cancer is the most common cancer in women and a leading cause of cancer death.
    • Incidence rises with age, especially after 50 years.
  • Risk Factors
    • Non-Modifiable: Female gender, age, family history of breast or ovarian cancer, BRCA1/2 mutations, and breast density.
    • Modifiable: Alcohol intake, obesity, sedentary lifestyle, nulliparity, and postmenopausal hormone replacement therapy.
Pathophysiology
  • Genetic Mutations
    • BRCA1 and BRCA2: Mutations significantly increase the risk of early-onset breast and ovarian cancers.
    • Other Genes: p53, PTEN, and CHEK2 are associated with sporadic cases.
  • Hormonal Influence
    • Estrogen and progesterone stimulate breast epithelial cell proliferation, contributing to tumor growth in ER/PR-positive cancers.
Clinical Manifestations
  • Palpable Mass
    • Most common presenting symptom, typically a firm, painless mass with irregular borders.
  • Skin and Nipple Changes
    • Skin dimpling, nipple retraction, or discharge (often bloody) may occur in advanced cases.
    • Inflammatory breast cancer presents with erythema, edema, and peau d’orange.
  • Axillary Lymphadenopathy
    • Enlarged lymph nodes may indicate regional metastasis.
breast cancer breast changes
Screening
  • Mammography
    • First-line screening tool, recommended biennially for average-risk women aged 40-74 by the US Preventive Services Task Force.
  • Breast MRI
    • Recommended annually for high-risk women (e.g., BRCA mutation carriers) as an adjunct to mammography.
Diagnosis
  • Imaging
    • Diagnostic Mammogram: Provides detailed imaging for symptomatic cases or abnormal screening results.
    • Ultrasound: Used to characterize cystic vs. solid masses and to evaluate axillary nodes.
  • Biopsy
    • Core Needle Biopsy: Preferred for diagnosis, allowing assessment of receptor status.
    • Fine-Needle Aspiration (FNA): May be used for palpable masses but provides limited histologic information.
Staging
  • TNM System
    • Based on tumor size (T), lymph node involvement (N), and distant metastasis (M).
    • Stages range from 0 (in situ) to IV (metastatic disease).
  • Prognostic Factors
    • Tumor grade, receptor status, HER2 status, and lymph node involvement impact prognosis and treatment planning.
Treatment
  • Surgery
    • Lumpectomy (Breast-Conserving Surgery): Removal of tumor with surrounding tissue, often followed by radiation.
    • Mastectomy: Complete removal of breast tissue, indicated for larger or multicentric tumors.
    • Sentinel Lymph Node Biopsy (SLNB): Assesses lymph node spread; axillary lymph node dissection may be added if positive.
  • Radiation Therapy
    • Used post-lumpectomy to reduce local recurrence risk and sometimes post-mastectomy if high-risk features are present.
  • Systemic Therapy
    • Hormonal Therapy: For ER/PR-positive tumors, using tamoxifen in premenopausal women and aromatase inhibitors in postmenopausal women.
    • Chemotherapy: Indicated for high-risk cases, TNBC, or HER2-positive tumors.
    • HER2-Targeted Therapy: Trastuzumab and other HER2-targeted agents improve outcomes in HER2-positive disease.
Key Points
  • Breast Cancer is the most common malignancy in women, with risk factors including age, genetics (BRCA mutations), and lifestyle factors.
  • Classification:
    • ER/PR-positive tumors respond to hormonal therapy.
    • HER2-positive tumors respond to HER2-targeted therapy.
    • TNBC lacks ER, PR, and HER2 expression and is treated with chemotherapy.
  • Screening: Mammography is the primary screening tool, with MRI added for high-risk patients.
  • Diagnosis involves clinical exam, imaging, and biopsy for histologic and receptor evaluation.
  • Staging follows the TNM system, and prognosis depends on tumor grade, receptor status, HER2 expression, and lymph node involvement.
  • Treatment includes surgery, radiation, and systemic therapies (hormonal, chemotherapy, HER2-targeted) based on tumor characteristics and stage.

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