Clinicopathological characteristics of metaplastic breast cancer - analysis of the basic immunohistochemical profile and comparison with other invasive breast cancer types.

INTRODUCTION: Metaplastic breast cancer (MpBC) is a rare but aggressive type of breast cancer accounting for 0.25-1% of all diagnosed invasive breast cancers. Morphologically, it is characterized by differentiation of the neoplastic epithelium into squamous cells and/or mesenchymal-looking tissue.

MATERIAL AND METHODS: We analyzed 13 MpBCs selected from the group of 1122 invasive breast cancers. Histopathological examination and analysis of estrogen (ER), progesterone (PR) and HER2 receptors expression in MpBC patients and their comparison to other types of invasive breast cancer has been performed.

RESULTS: 13 MpBC cases represented 1.16% of the 1122 invasive breast cancers. The MpBC group presented with a significantly larger tumor size (≥T2, 69% versus 49%, p < 0.001) and with higher grade of histological malignancy (G1-G3) (p < 0.001). MpBC group had significantly more cases with no hormone receptors (ER, PR) and HER2 overexpression/gene amplification compared with the other invasive breast cancer types group (ER-, 69% versus 23%, p < 0.001; PR-, 69% versus 28%, p < 0.001; HER2 0/1+, 93% versus 82%, p = 0.019). Most MpBCs (62%) were triple-negative. We found a correlation between hormone receptors expression and lymph node metastasis (p < 0.001). The analysis of the HER2 expression allowed us to find correlation between its expression and tumor histological grade (G1-G3) (p < 0.001), tumor size (T1a-T4) (p < 0.001) and lymph node metastasis (pN0-pN4) (p < 0.001) in MpBCs.

DISCUSSION: MpBCs are usually larger at primary diagnosis and most of MpBCs present with other poor prognostic indicators and show lack of steroid hormone receptors expression as well as HER2. Hormone receptor status and HER2 expression seems to correlate with histological grade of malignancy (G1-G3), tumor size (T1a-T4) and regional lymph node involvement (pN0-pN4) and these features are directly related to MpBC malignancy.