Breast carcinoma is the most common cancer in Egyptian women. Developing 
metastasis is the leading cause of death in patients with invasive ductal carcinoma of the breast. The 
epithelial–mesenchymal transition (EMT) plays an important role in breast cancer metastasis. Snail 1 
is a key regulator of the EMT of tumor cells. Aim: To study the immunohistochemical expression of 
Snail 1 in invasive ductal carcinoma NOS of the breast and their association with different 
clinicopathological features of breast IDC. Material and methods: This study comprised 70 cases of 
IDC-NOS of the breast. Formalin fixed and paraffin-embedded tissue sections from cases under 
investigation were subjected to haematoxylin and eosin staining and immunohistochemical staining 
for Snail 1 using the avidin biotin-peroxidase complex method. Results: Snail 1 immunostaining was 
nuclear. High snail 1 expression was detected in 52.86% of cases. High snail 1 expression was 
significantly associated with larger tumor size, higher tumor grade, higher lymph node stage, higher 
LNR, advanced tumor stage, poor Nottingham prognostic index (NPI), high Ki-67 PIs, high Her-2 neu 
expression, negative ER hormonal receptors, negative PR hormonal receptors and aggressive 
molecular subtypes being highest in triple negative and her-2 enriched types (P= 0.028, 0.003, 0.024, 
0.002, 0.001, 0.001, 0.001, 0.011, 0.002, 0.001, 0.002 respectively). High Snail 1 expression had 
significantly shorter OS (p <0.001) and poor DFS (p< 0.001). Snail 1 was independent prognostic 
indicators for OS (P= 0.03) and DFS (p<0.001). Conclusions: High snail 1 expression is associated 
with poor clinicopathological features of IDC of the breast, aggressive behavior of the tumor, shorter 
Os and Poor DFS.