Fibromatosis-like metaplastic carcinoma of breast: a challenge for clinicopathologic diagnosis

Abstract

Fibromatosis-like metaplastic carcinoma of breast (FLMC) is a newly described metaplastic tumor in the (4th) edition of the WHO classification of breast tumors in 2012. It is a low-grade tumor formed by spindle cells with mild or absent nuclear atypia, embedded in collagenized stroma, and it has only <5% tumor cells showing epithelial traits. Because its biological behavior is better than that of general spindle cell metaplastic cancer, this cancer type is added to the new WHO classification. Due to their mild morphology, breast FLMCs are often misdiagnosed as benign interstitial proliferative lesions or benign mesenchymal tumors. Accurate diagnosis is a challenging task particularly in needle core biopsies. We systematically reviewed 23 cases of metaplastic breast carcinoma (MBC), 8 cases of metaplastic carcinoma with squamous cell component, 12 cases of spindle cell/sarcomatoid metaplastic carcinoma, and 3 cases of FLMC. Also, we performed CK, CK high molecular weight (34βE12), CK7, CK5/6, P63, CD10, ER, PR, HER-2, SMA, Desmin, CD34, CD117, and S-100 immunohistochemistry, using Envision staining. This study was focused on clinical and pathological features of 3 FLMC cases and assessed the immunoprofile of MBC subtypes in a large series to improve the understanding of these diseases.

Keywords: Breast; diagnosis; fibromatosis-like metaplastic carcinoma; immunohistochemistry.

Figure 1

A. Low-grade fibromatosis-like spindle cells entrap normal breast glandular structures and surrounding fat tissue. (magnification, ×100). B. The cells are mainly arranged in fascicles and displayed tapering nuclei with mild anisonucleosis. (magnification, ×100). C. Some areas show cells with nuclei ranging from spindled to round or oval with discrete nucleoli. (magnification, ×400). D. Interstitial scattered lymphocytes, plasma cells, and other inflammatory cell infiltration. (magnification, ×100) (Hematoxylin and Eosin).

Figure 2

A. The neoplastic spindle cells are positive for CK protein. (magnification, ×100). B. The neoplastic spindle cells are positive for CK7 protein. (magnification, ×100). C. The neoplastic spindle cells are positive for P63 protein. (magnification, ×400). D. Ki-67 positive index was 15% to 20%; the index focally may be higher.