Breast Pathology Series Part 3: Stromal Tumors

Welcome to the third part of the breast pathology series, focusing on stromal tumors of the breast for undergraduate medical students.

Overview

• Discussion on benign stromal tumors: Fibroadenoma and Phyllodes Tumor.
• Exploration of intra-lobular and inter-lobular stromal tumors.

The Stroma of the Breast

• Intra-lobular Stroma: Located within lobules.
• Inter-lobular Stroma: Located between lobules.

Tumors of the Stroma

Intra-lobular Stromal Tumors

• Phyllodes Tumor
• Fibroadenoma
  • Classified as biphasic tumors due to the presence of a non-neoplastic epithelial component.
  • Growth factors from stromal cells promote epithelial proliferation.
  • Common mutation: MED12 gene.

Inter-lobular Stromal Tumors

• Lipoma
• Angiosarcoma (malignant)
• Myofibroblastoma
• Fibrous Tumors

Detailed Study of Intra-lobular Stromal Tumors

Fibroadenoma

• Most common benign tumor of female breast.
• Predominantly affects young and reproductive-age women.
• Mutations: Two-thirds of patients have MED12 mutations.
• Clinical Presentation: Solitary, mobile lump ("breast mouse"), can be multiple and bilateral.
• Hormone Sensitivity: Grow during pregnancy, regress post-menopause.
• Gross Features: Well-circumscribed, 3-4 cm, may extend to 10 cm.
• Microscopic Features: Mixture of epithelial and stromal tissue, predominance of fibrous tissue.
• Patterns:
  • Intracanalicular: Compression of ducts into slit spaces.
  • Pericanalicular: Ducts retain patency.
• Types:
  • Juvenile Fibroadenoma: Rapid growth in young women.
  • Complex Fibroadenoma: Associated with fibrocystic changes, slightly higher risk of malignancy.
  • Giant Fibroadenoma: Tumor size reaches 10 cm.

Risk of Malignancy in Fibroadenomas

• Simple Fibroadenomas: Slightly increased risk, but negligible.
• Complex Fibroadenomas and Older Women: Higher risk of subsequent malignancy.

Phyllodes Tumor

• Less common than fibroadenoma.
• Can be benign or malignant.
• Mutations:
  • Benign: MED12 mutation.
  • Malignant: Additional mutations like TERT gene.
• Gross Features: Large, bulbous protrusions, leaf-like cleft spaces.
  • Derived from Greek "phyllodes" meaning "leaf-like".
• Microscopic Features: Exaggerated intracanalicular growth with high stromal cellularity.
• Grading:
  • Low Grade (Benign): Mild features.
  • High Grade (Malignant): High cellularity, mitotic activity, and pleomorphism.
  • Borderline: Features between benign and malignant.
• Prognosis: Likely to recur without wide excision, mastectomy recommended for large tumors. High-grade lesions have hematogenous metastasis with stromal component only.

Tumors of Inter-lobular Stroma

Benign Tumors

• Myofibroblastoma
• Lipoma
• Fibromatosis

Malignant Tumors

• Angiosarcoma: Malignant tumor of blood vessels.

Conclusion

• Completed understanding of stromal tumors, focusing on intra-lobular and inter-lobular tumors.
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