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Background
Papillary lesions of the breast are categorized as solitary intraductal papilloma (IDP), multiple IDP, atypia-ductal carcinoma in situ (DCIS) within a papilloma, micropapillary DCIS, and papillary carcinoma. IDPs are benign breast lesions with propensity to upgrade on excision to atypical ductal hyperplasia and DCIS.

Educational Goals / Teaching Points
It is important to know the typical features of IDP and to recognize any variability in follow-up studies. Papilloma with atypical ductal hyperplasia (ADH) or DCIS can appear similar on all imaging modalities, but microcalcification within papilloma can represent DCIS and often aids in detection. Multiple IDPs have a higher rate of association with atypical lesions as noted by prior studies.

Key Anatomic/Physiologic Issues and Imaging Findings/Techniques
IDPs can be asymptomatic; when symptomatic they present as clear or bloody nipple discharge and are usually occult on mammography. Ultrasound often reveals either a focally dilated duct accompanied by an intraductal mass and a supplying blood vessel, or a circumscribed oval or round mass. Solitary IDPs located in the retro-areolar region usually present with bloody or clear nipple discharge, whereas multiple IDPs originating from terminal ductal lobular units are located peripherally and are rarely associated with nipple discharge.

Conclusion
On imaging, differentiating benign papillary tumors from malignant tumors is often difficult, with high rates of upgrade to atypical lesions on excision. Here we discuss cases of biopsy-proven IDPs that were upgraded to malignant tumors over varied periods of time.