Back
ditki Logo
medical & biological sciences

Breast Cancer for USMLE Step 2

Start your One-Week Free Trial
Already subscribed? Log in »
Breast Cancer for the USMLE Step 2 Exam
Definition and Classification
  • Definition
    • Breast cancer is a malignancy originating in breast tissue, often arising in the ducts (ductal carcinoma) or lobules (lobular carcinoma).
  • Classification by Receptor Status
    • Hormone Receptor-Positive (ER+ and/or PR+): Accounts for 70% of cases and responds well to hormonal therapy.
    • HER2-Positive: Expresses human epidermal growth factor receptor 2 (HER2); associated with more aggressive disease but responsive to HER2-targeted therapies.
    • Triple-Negative Breast Cancer (TNBC): Lacks ER, PR, and HER2 expression; more aggressive, and treated with chemotherapy.
Epidemiology and Risk Factors
  • Epidemiology
    • Breast cancer is the most common cancer in women and the second leading cause of cancer-related death among women.
  • Risk Factors
    • Non-Modifiable: Female gender, age, family history, BRCA1/2 mutations, early menarche, and late menopause.
    • Modifiable: Alcohol intake, obesity, hormone replacement therapy, physical inactivity, and nulliparity.
Pathophysiology
  • Genetic Mutations
    • BRCA1 and BRCA2: Germline mutations that significantly increase the risk for breast and ovarian cancers.
    • Other Genes: Mutations in p53, PTEN, and CHEK2 are associated with sporadic cases.
  • Hormonal Influence
    • Estrogen and progesterone play a role in stimulating breast epithelial cell proliferation, increasing the risk for ER-positive breast 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, and discharge (often bloody) may be present.
    • Inflammatory breast cancer presents with erythema, edema, and peau d’orange.
  • Axillary Lymphadenopathy
    • Enlarged lymph nodes may indicate metastatic spread to regional lymph nodes.
breast cancer breast changes
Screening
  • Mammography
    • Recommended every two years for average-risk women aged 40-74 years (USPSTF).
  • Breast MRI
    • Used as an adjunct in high-risk women, including BRCA mutation carriers, for annual screening alongside mammography.
Diagnosis
  • Imaging
    • Diagnostic Mammogram: Further evaluates abnormal screening results or symptomatic presentations.
    • Ultrasound: Helps characterize masses and assess axillary lymph nodes.
  • Biopsy
    • Core Needle Biopsy: Provides tissue for histology and receptor testing (ER, PR, HER2).
    • Fine-Needle Aspiration (FNA): May be used for palpable masses but lacks adequate tissue for receptor analysis.
Staging
  • TNM System
    • Based on tumor size (T), lymph node involvement (N), and distant metastasis (M), from Stage 0 (in situ) to Stage IV (metastatic).
  • Prognostic Factors
    • Tumor grade, receptor status (ER, PR, HER2), lymph node involvement, and tumor size guide treatment decisions and prognosis.
Treatment
  • Surgery
    • Lumpectomy (Breast-Conserving Surgery): Removes tumor with a margin of normal tissue, usually followed by radiation.
    • Mastectomy: Complete removal of breast tissue, often preferred in larger or multicentric tumors.
    • Sentinel Lymph Node Biopsy (SLNB): Assesses lymph node involvement; axillary lymph node dissection may be done if SLNB is positive.
  • Radiation Therapy
    • Typically used post-lumpectomy to reduce local recurrence and may be considered post-mastectomy in high-risk cases.
  • Systemic Therapy
    • Hormonal Therapy: Used for ER/PR-positive tumors; includes tamoxifen (premenopausal) and aromatase inhibitors (postmenopausal).
    • Chemotherapy: Often used for high-risk tumors, TNBC, or HER2-positive cancers.
    • HER2-Targeted Therapy: Trastuzumab and other HER2 inhibitors are effective for HER2-positive tumors.
Key Points
  • Breast Cancer is classified by hormone and HER2 receptor status, guiding treatment choices and prognosis.
  • Screening:
    • Mammography is the main screening tool, with MRI added for high-risk patients.
    • Recommended biennially from age 40-74 for average-risk women.
  • Diagnosis includes clinical exam, imaging, and biopsy for histology and receptor status determination.
  • Staging is based on the TNM system, with prognosis influenced by tumor grade, receptor status, and lymph node involvement.
  • Treatment:
    • Surgery, radiation, and systemic therapy (hormonal, chemotherapy, HER2-targeted) are based on tumor characteristics and stage.

Related Tutorials