A 48-year-old woman from Mumbai presents with a 6-month history of bloody nipple discharge from the left breast. On examination, there is a subareolar mass, 1.5 cm, non-tender. Mammography is unremarkable. Histopathology of the excised lesion shows a single layer of epithelial cells with myoepithelial cells lining a dilated duct filled with blood and necrotic material. The lesion is confined within the duct and does not breach the basement membrane. What is the most likely diagnosis?

Explanation

## Intraductal Papilloma: Clinical and Pathological Features **Key Point:** Intraductal papilloma is a benign, solitary lesion arising within a lactiferous duct, presenting with spontaneous bloody or serous nipple discharge. It is the most common cause of pathological nipple discharge in women. ### Clinical Presentation of Intraductal Papilloma | Feature | Intraductal Papilloma | DCIS | Invasive Carcinoma | |---------|----------------------|------|--------------------| | **Nipple discharge** | Spontaneous, bloody/serous, single duct | Rare; usually bloody | Rare; bloody | | **Palpable mass** | Yes (subareolar, 0.5–2 cm) | Usually not palpable | Yes, firm/hard | | **Mammography** | Often normal | Microcalcifications, mass | Dense mass, calcifications | | **Basement membrane** | Intact | Breached (malignant) | Breached (malignant) | | **Myoepithelial layer** | Preserved | Absent/disrupted | Absent | | **Malignant potential** | <5% (if solitary) | 20–50% → invasive | Already invasive | ### Pathological Hallmarks of Intraductal Papilloma **High-Yield:** The **intact basement membrane** and **preserved myoepithelial layer** are the defining features that distinguish benign intraductal papilloma from DCIS and invasive carcinoma. 1. **Epithelial fronds:** Papillary projections lined by a single layer of ductal epithelium. 2. **Myoepithelial cells:** Present at the base, forming a complete layer around the lesion. 3. **Basement membrane:** Intact; no invasion beyond the duct. 4. **Necrosis:** May be present (as in this case) due to outgrowth of blood supply. 5. **Atypia:** Usually absent; nuclei are bland and regular. ### Why This Case Is Intraductal Papilloma - **Subareolar location:** Classic for papilloma (usually central ducts). - **Bloody nipple discharge:** Pathognomonic for papilloma. - **Intact basement membrane:** Confirms benignity. - **Preserved myoepithelial layer:** Rules out DCIS and invasive disease. - **Single duct involvement:** Solitary papillomas have <5% malignant potential. **Clinical Pearl:** A solitary intraductal papilloma with benign features on histology requires **excision with clear margins** and **clinical follow-up**, but does NOT require mastectomy. Multiple papillomas or those with atypia carry higher malignant risk. **Mnemonic:** **PAPILLOMA** = **P**apillary fronds, **A**pical necrosis, **P**reserved myoepithelium, **I**ntact basement membrane, **L**ocal (subareolar), **L**imited malignant potential, **O**ften bloody discharge, **M**ass palpable, **A**typical features absent.