The terminology can be confusing. I’ll try to add pictures/diagrams to clarify at a later date. Feel free to ask questions.
Intraductal papilloma – duct structures with broad fibrovascular cores lined by an myoepithelial and epithelial lining. May be solitary in the subareolar region (50-60 yrs typically) and multiple in the periphery ( 20-30 yrs typically). May be associated with UEH, ADH, DCIS, apocrine or squamous metaplasia. Surrounding fibrotic stroma may give the impression of pseudoinvasion and myoepithelial cells stains will be helpful in differentiating. DD includes papillary Dcis, encapsulated papillary ca and invasive ca. When there is an area of low grade atypical proliferation (adh vs lg dcis only – size criterion cut off of 3mm as per Page et al study can be used) But only for adh vs lg dcis distinction and not to be used for intermediate and hg dcis.
Entities: Benign papilloma, Papilloma with ADH, Papilloma with DCIS (care to differentiate from papillary dcis), carcinoma arising in a papilloma
Encapsulated/ encysted papillary carcinoma – a rare type of carcinoma which is relatively indolent. A well circumscribed papillary lesion with a fibrous rim and no evidence of stromal invasion however lacking a myoepithelial layer of the cells lining the fibrous cores and also lacks a myoepithelial layer at the peripheral rim compared to papillary carcinoma in situ which retains the myoepithelial layer at the rim. Encysted papillary carcinoma shows papillary cores lined by a single epithelial layer usually. This may be columnar but there may be unusual variants with a secretory endometrial appearance or an appearance of thyroid papillary carcinoma. To differentiate EPC myoepithelial markers will be negative at the fibrovascular cores and also at the periphery, and will usually show uniform ER positivity. The differential includes: benign papilloma, papillary carcinoma in situ, papilloma with dcis, papillary dcis, metastatic papillary carcinoma (thyroid and ovarian -check history), cystic degeneration of carcinoma (look for high nuclear grade and necrosis has a poor prognosis) and invasive papillary carcinoma (presence of desmoplastic stroma and mucin stains may help) (NB There can be encysted papillary carcinoma with pseudoinvasion especially due to fibrosis from needle core biopsies – care to withhold diagnosis of nst which is more common than invasive papillary)! EPC considered as a carcinoma with a pushing border and with a low risk of lymph node and visceral metastasis.
Solid papillary carcinoma– what a solid variant of EPC would look like. Carcinoma with a pushing border. Solid papillary carcinoma is characterized by well-circumscribed expansile nodules consisting of sheets of malignant epithelial cells supported by papillae, although these are often inconspicuous. The epithelial cells are typically ovoid or spindle-shaped and polarize around the fibrovascular cores. They may exhibit a streaming pattern similar to that seen with usual epithelial hyperplasia. Intracellular and extracellular mucin is commonly present and when accompanied by invasive carcinoma, the latter is often invasive mucinous carcinoma. The cells may exhibit neuroendocrine features and staining with chromogranin and synaptophysin can be seen. As with encapsulated papillary carcinomas, myoepithelial cells are typically not identified with immunohistochemical stains at the periphery of these tumors or lining the fibrovascular cores. This raises the possibility that these tumors represent invasive carcinomas with pushing borders rather than in situ processes; however, they tend to follow an indolent course, especially when there is no evidence of unequivocal stromal invasion.
Papilloma with focal atypia and atypical papilloma are unhelpful terms – not specific.
Breast Pathology: O Malley, Pinder and Mulligan