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17 August 2022 - Case of the Month #518

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Thanks to Drs. Mariel Molina Nunez and Julie Jorns, Medical College of Wisconsin, Milwaukee, Wisconsin, USA, for contributing this case and discussion and to Dr. Kristen Muller, Dartmouth Geisel School of Medicine, Lebanon, New Hampshire, USA for reviewing the discussion.

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Case of the Month #518

Clinical history:
A postmenopausal woman, on a screening mammogram, was found to have a 15 mm mass in the lower inner quadrant of the left breast. Breast ultrasound revealed a 1.7 cm complex solid and cystic mass.

Radiology and histopathology images:

What is your diagnosis?

Click here for diagnosis, test question and discussion:

Diagnosis: Encapsulated papillary carcinoma of the breast with lobular differentiation

Test question (answer at the end):
In which group is encapsulated papillary carcinoma of the breast most commonly seen?

A. Childhood (≤ 18 years)
B. Lactating / pregnant
C. Men
D. Postmenopausal women



Encapsulated papillary carcinoma (EPC) is a rare malignancy accounting for 0.5 - 1% of all breast cancers. EPC has a predominantly indolent course and is currently considered a subset of in situ breast carcinoma (Am J Surg Pathol 2011;35:1093, Ann Diagn Pathol 2020;49:151613). EPC can occur in a wide age range but most commonly presents in elderly women (Am J Surg Pathol 2011;35:1093). EPCs usually consist of a single nodule but multinodular cases have been described (Mod Pathol 2021;34:1044).

Macroscopically, this entity presents as a solid mass with surrounding cystic space and a thick, encircling fibrotic capsule (Arch Pathol Lab Med 2016;140:1052). Microscopically, a key feature is the absence of myoepithelial cells, both within, as well as at the periphery of the neoplasm, despite current classification as in situ breast carcinoma (Am J Clin Pathol 2005;123:36, Am J Surg Pathol 2006;30:1002).

The microscopic features are identical to that of DCIS within an intraductal papilloma or papillary DCIS; however, DCIS morphology is present throughout the lesion and the lesion is typically larger and expansile. Like atypia and DCIS, the carcinomatous epithelium in EPC is negative for CK5/6. EPCs are usually low to intermediate grade and, accordingly, are diffusely and strongly ER positive. However, high grade EPCs with more variable ER staining are occasionally encountered (Histopathology 2015;66:740).

In the absence of frank invasion beyond the fibrous capsule, EPC is staged as in situ carcinoma (pTis) and managed accordingly (Mod Pathol 2021;34:78). However, some encapsulated papillary carcinomas may have associated invasive components, which are usually of the ductal type and, when present, should be staged according to the greatest dimension of invasive ductal carcinoma (Histopathology 2016;68:45).

Cases of invasive lobular carcinomas with encapsulated papillary carcinoma growth patterns have been previously reported (Breast Cancer 2021;28:1383, Pathobiology 2016;83:2213, Breast J 2020;26:1231).

EPC with lobular differentiation has only been recently described (Lab Invest 2022;102:79). The background breast in our case showed abundant atypical lobular hyperplasia (ALH), providing a clue to lobular differentiation in the EPC. Immunohistochemical stains revealed loss of myoepithelium via p63 and calponin immunohistochemistry (not pictured) and E-cadherin was negative throughout the lesion, supporting lobular differentiation.

Test question answer:

D. Postmenopausal women. Encapsulated papillary carcinoma (EPC) of the breast is an uncommon breast cancer that is classified as in situ, is typically low to intermediate grade and most frequently occurs in elderly, postmenopausal women rather than in younger women. EPCs constitute a slightly higher proportion of breast cancers in male patients as compared to female patients. However, male breast cancer is uncommon and is most frequently invasive ductal carcinoma (comprising about 85% of male breast cancers).

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