Breast Fibroadenoma

Breast fibroadenomas are benign, solid tumors made of stromal and epithelial elements.

Epidemiology

• Second most common tumor in the breast
• Most common tumor in women < 30 years
• Rare in women > 40 years

Pathogenesis

• Stromal overgrowth with collagen arranged in “swirls”
• Thought to be influenced by ovarian hormones

History

• Painless breast mass 
• Changes with menstrual cycle (grow with pregnant or hormone therapy; shrink after menopause)

Physical Exam

• Mass often occurs in upper outer quadrant of the breast
• Mass characteristics
  • Unilateral
  • Nontender/painless
  • Firm, rubbery
  • Well-circumscribed
  • Smooth or lobulated 

Imaging

• Initial imaging
  • Age < 30 → breast US
  • Age 30 – 39 → either breast US or diagnostic mammogram
  • Age ≥ 40 → diagnostic mammogram
• Core needle biopsy if initial imaging yields suspicious findings
• Mammography isn’t helpful for distinguishing between breast cysts and fibroadenomas
• Findings:
  • Breast US: oval or round hypoechoic mass with circumscribed border
  • Mammogram: oval or round mass with circumscribed margin, can have coarse calcifications (popcorn lesions) from degeneration 

Treatment

• Generally
  • Small fibroadenomas → observed
  • Large/growing fibroadenomas → surgical excision 
• When a tissue diagnosis confirms fibroadenoma, surgical excision isn’t needed
• Patients ≤ 35 years → need the following to qualify for observation (and not require excision)
  • Mass characteristics: firm, rubbery, rolls, not fixed
  • US or mammogram consistent with fibroadenoma
  • Needle core biopsy consistent with fibroadenoma
• Patients > 35 years → excisional biopsy to ensure diagnosis (or core needle biopsy if attempting 1-step surgery)
• Surgical excision
  • Reveals a well-encapsulated mass that easily detaches from surrounding breast tissue (if it’s a fibroadenoma)
  • Surgical techniques
    • Lumpectomy or excisional biopsy
    • Cryoablation
  • Contraindications to surgical excision: fibroadenomas < 2 cm

Relevant Information

• Most common breast lesion in adolescents and young women
• Fibroadenoma subtypes
  • Simple fibroadenoma
    • Most common
    • Don’t increase risk of cancer
    • Often present as palpable mass
    • Usually smaller (< 3 cm)
  • Complex fibroadenoma
    • Slightly increased risk of cancer
    • Complex if any of the following
      • Epithelial calcification
      • Apocrine hyperplasia/metaplasia
      • Sclerosing adenosis
      • Breast cysts
    • Treat with excisional biopsy
  • Giant fibroadenoma
    • > 5 cm (unusually large)
    • Rapid growth
    • Need to rule out phyllodes tumor
  • Juvenile fibroadenoma
    • Large fibroadenoma in women ages 10 – 18 years old 
    • Histologically more cellular than a usual fibroadenoma
  • Tubular fibroadenoma: tightly packed epithelial component with sparse connective tissue; benign
• Histology: fibrous tissue compressing epithelial cells

• Breast anatomy
  • Lies between subdermal layer of adipose tissue and superficial pectoral fascia
  • Cooper ligaments
    • Provide structural support and shape (anchored into the skin)
    • Infiltration by tumors can produce tethering, resulting in dimpling on the breast tissue
• Lymphatics
  • Lymph nodes
    • Level 1: located lateral to the lateral border of the pectoralis minor muscle
    • Level II: located posterior to the pectoralis minor muscle as well as anterior to the pectoralis minor and posterior to the pectoralis major (Rotter or interpectoral nodes)
    • Level III: located medial to pectoralis minor muscle and include subclavicular nodes
  • Most drains to axillary nodes (97%)
  • Any quadrant can drain into internal mammary nodes
  • Supraclavicular nodes → N3 disease
  • Primary axillary adenopathy → ≤ 1 is lymphoma
• Nerves
  • Long thoracic nerve
    • Innervates serratus anterior muscle 
    • Injury → winged scapula 
    • Lateral thoracic artery supplies serratus anterior muscle
  • Thoracodorsal nerve
    • Innervates latissimus dorsi muscle
    • Injury → weak arm pull-ups and adduction
    • Thoracodorsal artery supplies latissimus dorsi
    • Arises from posterior cord of brachial plexus; enters axillary space under axillary vein (close to long thoracic nerve)
  • Medial pectoral nerve: innervates innervates pectoralis major and pectoralis minor muscles
  • Lateral pectoral nerve: innervates pectoralis major muscle
  • Intercostobrachial nerve
    • Lateral cutaneous branch of second intercostal nerve
    • Sensation to medial arm and axilla
    • Most common injured nerve with modified radical mastectomy (MRM) or axillary lymph node dissection (ALND)
• Arterial supply: branches of
  • Internal thoracic (mammary) artery
  • Intercostal arteries
  • Thoracoacromial artery
  • Lateral thoracic artery
• Batson’s plexus: valveless vein plexus, allows direct hematogenous metastasis of breast cancer to spine
• Costoclavicular ligament (Halsted ligament): defines axilla apex
• Breast development
  • Formed from ectoderm milk streak
  • Hormone influence
    • Estrogen: duct development (double layer of columnar cells)
    • Progesterone: lobular development
    • Prolactin: synergizes estrogen and progesterone
    • Cyclic changes
      • Estrogen → increased breast swelling, growth of glandular tissue
      • Progesterone → increased maturation of glandular tissue, withdrawal causes menses
      • FSH, LH surge → ovum release
      • After menopause, less estrogen and progesterone results in atrophy of breast and vulvar tissue
• Microscopic anatomy
  • Three tissue types
    • Glandular epithelium
      • Branching system of ducts arranged in a radial pattern extending from the nipple-areolar complex
      • Each major duct has branches and ultimately ends in terminal ductules or acini (acini are milk-forming glands of lactating breasts)
    • Fibrous stroma and supporting tissues
    • Adipose tissue 
  • Basement membrane
    • Contains laminin, type IV collagen, proteoglycans
    • Differentiates in situ from invasive breast cancer

Complications

• Lobular carcinoma in situ (50%): stage 0
• Invasive carcinomas (35%)
• Intraductal carcinoma (15%)
• Breast cancer → rare (0.2%) in newly discovered fibroadenomas

Differential Diagnoses

• Breast cyst
• Breast carcinoma
• Phyllodes tumor
• Breast lymphoma
• Metastasis to breast from another primary site

Resources

• The American Society of Breast Surgeons. “Choosing Wisely: Benign Breast Disease,” (2023)