10.6 Breast Pathology & Clinical Breast Disease

Breast Pathology in the Step 2 CK Reproductive Domain

Female reproductive content specifications include breast disorders alongside gynecologic pathology. Step 2 CK items test screening thresholds, evaluation of palpable masses, differentiation of benign versus malignant lesions, and initial cancer management guided by receptor status.

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Breast Cancer Screening & Risk Stratification

Average-Risk Screening

For average-risk women, the USPSTF (2024) recommends biennial screening mammography from ages 40 to 74 years. Clinical breast examination alone is not an adequate substitute for mammography in screening-age patients.

Elevated-Risk Features

High-risk factors that alter surveillance and prevention counseling include:

• Pathogenic BRCA1 or BRCA2 variants (also elevated ovarian cancer risk)
• Strong family history / known hereditary cancer syndromes
• Prior thoracic radiation (e.g., Hodgkin lymphoma treatment)
• Atypical ductal or lobular hyperplasia; lobular carcinoma in situ (LCIS)
• Extremely dense breasts (affects mammographic sensitivity)

High-risk patients may need earlier and more intensive imaging (annual mammography ± breast MRI) and genetic counseling referral. Risk-reducing strategies include enhanced surveillance, chemoprevention (tamoxifen, raloxifene, or aromatase inhibitors in selected patients), and, for BRCA carriers, discussion of risk-reducing mastectomy and salpingo-oophorectomy.

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Evaluation of a Palpable Breast Mass

Any new palpable breast mass requires age-appropriate diagnostic imaging—not routine screening protocols.

              [ Palpable breast mass ]
                         |
          +--------------+--------------+
          |                             |
   [ Age <30–35 years ]          [ Age ≥30–35 years ]
          |                             |
   [ Ultrasound first ]        [ Diagnostic mammography + ultrasound ]
          |                             |
          v                             v
   [ Simple cyst ]              [ BIRADS assessment ]
          |                             |
   [ Aspiration if           +----------+-----------+
    symptomatic]             |                      |
                      [ BIRADS 1–3 ]          [ BIRADS 4–5 ]
                             |                      |
                      Observe / short-     [ Core-needle biopsy ]
                      interval follow-up           |
                                           [ Pathology-guided therapy ]

• BIRADS 1–2: Benign; routine follow-up.
• BIRADS 3: Probably benign; short-interval imaging follow-up (typically 6 months).
• BIRADS 4–5: Suspicious/highly suggestive; image-guided core-needle biopsy is required.
• Never rely on a "reassuring" exam alone in a patient with a persistent mass and discordant imaging.

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Benign Breast Disease

Fibroadenoma

Most common benign solid breast tumor in adolescents and young women. Presents as a mobile, rubbery, well-circumscribed, nontender mass. Ultrasound shows a homogeneous, well-circumscribed solid lesion. Management is observation with serial exam/imaging if classic, or core biopsy/excision if atypical, enlarging, or patient preference.

Breast Cysts

Common in peri-menopausal women. Ultrasound distinguishes simple from complex cysts. Simple cysts with nonbloody aspirate that resolve completely are benign. Bloody aspirate, incomplete resolution, or complex cystic-solid lesions require further evaluation and biopsy.

Fibrocystic Changes

Cyclic bilateral breast pain and nodularity that fluctuate with the menstrual cycle. Supportive care includes a well-fitting bra, NSAIDs, and avoidance of unnecessary imaging for classic cyclic symptoms without dominant mass.

Intraductal Papilloma

Most common cause of unilateral bloody nipple discharge from a single duct. Evaluate with ultrasound ± mammography and duct excision for definitive diagnosis and to exclude occult malignancy.

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Mastitis & Breast Abscess

Lactational mastitis typically occurs in breastfeeding patients within the first few months postpartum. Presents with unilateral breast pain, erythema, induration, and systemic symptoms (fever, malaise). Most common organism is Staphylococcus aureus.

Always counsel continued milk removal. Do not "rest" the breast. If mastitis does not improve within 48–72 hours or inflammatory features persist, reassess for abscess or inflammatory carcinoma.

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Breast Cancer: Presentation & Initial Management

Histologic & Molecular Subtypes

• Invasive ductal carcinoma (IDC): Most common invasive subtype (~70–80%).
• Invasive lobular carcinoma: May present with subtle findings; spreads in single-file pattern.
• Ductal carcinoma in situ (DCIS): Noninvasive; often detected as mammographic microcalcifications.
• Receptor profiling (mandatory on invasive cancer):
  • ER/PR positive: Endocrine therapy (tamoxifen in premenopausal; aromatase inhibitor in postmenopausal; ovarian suppression strategies in selected premenopausal high-risk patients).
  • HER2 positive: Anti-HER2 therapy (trastuzumab ± pertuzumab) with chemotherapy.
  • Triple-negative (ER−/PR−/HER2−): Chemotherapy backbone; immunotherapy in selected early and advanced settings.

Local Therapy Principles

• Early-stage disease: breast-conserving surgery (lumpectomy) plus radiation is equivalent to mastectomy for survival in appropriately selected patients.
• Axillary staging uses sentinel lymph node biopsy for clinically node-negative disease.
• Neoadjuvant systemic therapy is used for larger tumors, node-positive disease, HER2-positive, or triple-negative subtypes to enable breast conservation and assess response.

Metastatic Patterns to Remember

Breast cancer commonly metastasizes to bone, lung, liver, and brain. Bone metastases may present with pathologic fracture or hypercalcemia. New focal neurologic deficits in a patient with breast cancer history warrant urgent CNS imaging.

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Clinical Decision Pearls for Exam Vignettes

1. A dominant mass in a woman ≥30–35 years → diagnostic mammography + ultrasound, not screening mammogram alone.
2. BIRADS 4–5 → core biopsy, not empirical observation.
3. Postpartum fever + breast erythema without fluctuance → mastitis antibiotics and continued breastfeeding.
4. Peau d'orange and nonresolving inflammation → consider inflammatory breast cancer and biopsy skin.
5. ER+/PR+ disease → endocrine therapy is a cornerstone of adjuvant treatment.
6. Unilateral bloody single-duct discharge → evaluate for intraductal papilloma and occult carcinoma.