genotoxin-dependent suppression of breast cancer-initiating cell growth. Immunohistochemical assessment of Her2- negative tumors revealed significant association with overexpression of Notch1 and Notch3. Knockdown of Notch pathway resulted in sensitization of breast cancer cells to deionizing

Whereas the Her2/neu/erbB2 receptor (Her2) could be a molecular target of the receptor-positive breast cancer, the therapeutic targets of Her2-negative cancer largely remain to be established. The expression of Her2 was evaluated in 48 primary breast cancer tumors by immunohistochemistry. The identified Notch pathway was studied in genotoxin-dependent suppression of breast cancer-initiating cell growth. Immunohistochemical assessment of Her2negative tumors revealed significant association with overexpression of Notch1 and Notch3. Knockdown of Notch pathway resulted in sensitization of breast cancer cells to deionizing radiation, leading to cell death; the effect was more significant in stem marker CD44+ than in CD44cells, and more profound in the Her2-negative than in positive cancer cells. The present study indicates that inhibition of Notch signaling could antagonize survival signal of Her2-negative breast cancer-initiating cells carrying genomic damage, and suggests that targeted suppression of the Notch pathway may give the rationale for sensitizing Her2-negative cancerinitiating cells to a therapeutic approach.