High‐grade encapsulated papillary carcinoma of the breast: an under‐recognized entity

Encapsulated papillary carcinoma (EPC) is a recognized special type of breast carcinoma. Despite compelling evidence indicating its invasive nature, although not of a conventional form, the current consensus is to manage EPC as an in-situ disease, based on its indolent clinical behaviour. Although most EPCs are recognized to be of low and intermediate grade, a distinct proportion of these tumours do show high cytonuclear grade features. The existence and behaviour of these rare high-grade variants remains to be defined. We aim to characterise these tumours and provide evidence to guide their management.In this study, we have identified 12 high-grade EPCs without associated conventional stromal invasion. To further characterize these high-grade tumours, a series of invasive papillary carcinomas (n = 30) were assessed for the coexistence of EPC. The literature was also reviewed. Approximately 3% of pure EPCs showed high-grade features as defined by nuclear pleomorphism and increased mitotic activity. These tumours not only showed histological features associated with aggressive behaviour, but were also often hormone receptor-negative, tended to be of larger size, and were more frequently associated with stromal invasion. Of the 10 patients with follow-up data, one with pure high-grade EPC developed recurrence and died of her disease.High-grade EPC is rare, and its histological features and more aggressive clinical behaviour suggest that consideration should be given to managing it in a similar fashion to conventional forms of invasive breast carcinoma, based on established clinicopathological parameters.