Encapsulated Papillary Carcinoma of the Breast: Imaging Features with Histopathologic Correlation.

Encapsulated papillary carcinoma (EPC) is a rare, clinically indolent breast malignancy most common in postmenopausal women. Absence of myoepithelial cells at the periphery is a characteristic feature. Mammographically, EPC typically presents as a mostly circumscribed, noncalcified, dense mass that can have focally indistinct margins when there is associated frank invasive carcinoma. Ultrasound shows a circumscribed solid or complex cystic and solid mass, and occasional hemorrhage in the cystic component may produce a fluid-debris level; the solid components typically show intense washout enhancement on MRI. Color Doppler may demonstrate a prominent vascular pedicle and blood flow within solid papillary fronds. Encapsulated papillary carcinoma can exist in pure form; however, EPC is often associated with conventional ductal carcinoma in-situ and/or invasive ductal carcinoma, no special type. Adjacent in-situ and invasive disease may be only focally present at the periphery of EPC and potentially unsampled at core-needle biopsy. In order to facilitate diagnosis, the mass wall should be included on core-needle biopsy, which will show absence of myoepithelial markers. Staging and prognosis are determined by any associated frankly invasive component, with usually excellent long-term survival and rare distant metastases.