A 58-year-old woman from Mumbai presents with a 6-month history of spontaneous bloody nipple discharge from the left breast. Physical examination reveals a palpable mass beneath the areola. Mammography and ultrasound show a 1.2 cm mass in the subareolar region with dilated ducts. Ductography reveals a filling defect in the major duct. Excisional biopsy of the mass and involved duct is performed. Histopathology shows a papillary lesion with a fibrovascular core lined by epithelial cells without atypia, and intact myoepithelial layer. What is the diagnosis?

Explanation

## Histopathologic Diagnosis **Key Point:** The intact myoepithelial layer and absence of atypia are the defining features that distinguish a benign intraductal papilloma from papillary carcinoma. ## Differential Diagnosis: Papillary Lesions of the Breast | Feature | Intraductal Papilloma | Papillary Carcinoma | DCIS (Papillary) | |---------|----------------------|-------------------|------------------| | **Myoepithelial layer** | Intact, present | Absent or disrupted | Absent | | **Cytologic atypia** | Absent | Present (high-grade nuclei) | Present | | **Fibrovascular core** | Yes, well-formed | Yes, but with atypical epithelium | Yes, but with necrosis | | **Location** | Subareolar, major ducts | Can be anywhere | Can be anywhere | | **Nipple discharge** | Bloody, spontaneous | Bloody or serous | Bloody | | **Age** | 40–60 years | 50–70 years | Variable | | **Malignant potential** | <5% (solitary), ~20% (multiple) | Malignant by definition | Malignant by definition | | **Treatment** | Excision of involved duct | Mastectomy or wide excision + RT | Mastectomy or wide excision + RT | ## Key Diagnostic Criteria **High-Yield:** The **intact myoepithelial layer** (demonstrated by immunohistochemistry for p63 or smooth muscle actin) is the single most important feature distinguishing benign intraductal papilloma from malignant papillary carcinoma. **Mnemonic: PAPILLOMA Features** — **P**apillary structure, **A**typia absent, **P**erfect myoepithelium, **I**ntraductal location, **L**ocal excision curative, **L**ow malignant potential, **O**lder women, **M**ajor ducts, **A**lways benign (if solitary). **Clinical Pearl:** Spontaneous bloody nipple discharge is the classic presentation of intraductal papilloma. The discharge is typically unilateral and from a single duct. Ductography or ductoscopy can identify the lesion, and excision of the involved duct is both diagnostic and therapeutic. ## Pathologic Features in This Case 1. **Papillary lesion with fibrovascular core** — characteristic architecture 2. **Epithelial cells without atypia** — benign cytology 3. **Intact myoepithelial layer** — the definitive benign finding 4. **Subareolar location** — typical for solitary papilloma 5. **Dilated ducts** — result of obstruction by the papilloma **Warning:** Do not confuse intraductal papilloma with papillary carcinoma based on the presence of a papillary structure alone. The myoepithelial layer status is the critical differentiator.