Multiple Cystic Components With Bleeding Are Important Diagnostic Findings for Encapsulated Papillary Carcinomas of the Breast: A Case Report.

Encapsulated papillary carcinoma (EPC) is a rare papillary breast lesion with known favorable biology, but is not fully understood of its image findings. A 78-year-old woman with a screening mammography-detected breast mass was referred to our hospital. Mammography showed an oval mass, 4.3 cm in size, with circumscribed margins in her left breast. Ultrasound showed that the mass consisted of high-echo areas and many cystic areas. Magnetic resonance imaging (MRI) of the mass showed weak high signals in some areas on T1-weighted images and mixed high and low signals with fluid-fluid level formation on T2-weighted images. Core needle biopsy pathologically showed cancer cells growing in low papillary and papillary fashions and had microvoids around cancer cells, leading to the suspected diagnosis of invasive micropapillary carcinoma (IMPC). The patient, therefore, underwent a partial mastectomy and a sentinel node biopsy. The tumor was completely encapsulated with a fibrous capsule and consisted of cancer cells growing in cribriform, papillary, and low papillary fashions with cystic structures and intracystic bleeding. Immunostaining showed estrogen receptor positivity (Allred score 8), progesterone receptor positivity (Allred score 7), human epidermal growth factor receptor type 2 equivocality (fluorescence in-situ hybridization negative), a Ki-67 labelling index of 17%, and no myoepithelial cells, leading to the final diagnosis of EPC. The patient recovered uneventfully and has been well on adjuvant aromatase inhibitor therapy for 14 months. Diagnostic physicians should note that multiple cystic components with bleeding in the mass may be an important diagnostic clue to differentiate EPC from other papillary or pseudopapillary breast disorders, including IMPC.