Benign breast lesions that mimic malignancy

Many benign and reactive lesions of the breast show morphological overlap with malignant lesions. These benign mimics of malignancy often present diagnostic challenges to even the most experienced pathologists. This review focuses on several benign lesions of the breast that mimic malignant entities. For each of these lesions, we describe the key morphological and immunohistochemical features, potential diagnostic pitfalls, and our approach to arriving at the correct diagnosis.

Epithelioid Myofibroblastoma of the Breast: A Report of Two Cases with Discussion of Diagnostic Pitfalls

Mesenchymal lesions of the breast are uncommon lesions which present diagnostic dilemmas for even the most experienced pathologists. Here, we present two cases of the epithelioid-variant of myofibroblastoma which were misdiagnosed as malignant lesions. Careful integration of clinical presentation, imaging, and close examination of the gross, histologic, and immunohistochemical findings can assist in differentiating these challenging lesions and avoiding diagnostic pitfalls.

Diagnostic challenges of intra-operative frozen consultation for mammary epithelioid myofibroblastoma

Myofibroblastoma (MFB) of the breast is a rare benign neoplasm that exhibits several morphologic variants and presents diagnostic challenges for pathologists, especially in recognizing intra-operative frozen sections. In order to raise awareness of this tumor and avoid misdiagnosis, we describe a case of a 38-year-old female patient diagnosed as epithelioid MFB. This painless tumor was well-circumscribed, found in the left breast and was physically examined over a period of six months. Histologically, this tumor was predominantly composed of epithelioid cells, which arranged as single cells, small clusters or nests. Tumor stroma was collagenized with spindle cells, adipose and focal myxoid areas. This case was misinterpreted as invasive carcinoma in the frozen section. The immunohistochemical profile demonstrated positivity for Vimentin, desmin, SMA, calponin, CD34, ER, PR and AR, whereas pan-keratin, keratin 7, keratin 34βE12, keratin 5/6, EMA, p63 and S100 were negative. RB1 was abnormally negative, confirming the diagnosis of epithelioid MFB. Making a correct diagnosis is primarily dependent on awareness by the pathologist of this unusual variant of MFB and careful integration of clinicopathologic findings to avoid potential diagnostic pitfalls.

Mammary epithelioid myofibroblastoma mimicking invasive carcinoma: case report and literature review

Myofibroblastoma (MFB) of the breast is a rare benign neoplasm, which exhibits several morphologic variants and presents diagnostic dilemmas for pathologists. Here, we describe a case of a 42-year-old female patient diagnosed as epithelioid MFB. This painless tumor was well-circumscribed and found in the left breast for three months. Histologically, this tumor was predominantly composed of epithelioid cells, which arranged as single cells or small clusters, and formed a cellular nodule. Tumor stroma was collagenized, with scattered myxoid areas. This case was misinterpreted as invasive lobular carcinoma in the original diagnosis. Immunohistochemical profile demonstrated positivity for desmin, SMA, calponin, CD34 and hormone receptors, whereas pan-CK, CK7, CK8, CK34bE12, CK5/6, EMA, p63 and S-100 were negative, confirming the diagnosis of epithelioid MFB. Awareness of this unusual variant and careful integration of clinicopathologic findings would be critical to diagnosis this challenging lesion and avoid potential diagnostic pitfalls.