NOTCH1 and neoplasm: However, double edge function of Notch1 do exist, not only because there are strong lines of evidence as suppressor[47], [49], but also because about one fourth of the tumors in our study were negative for Notch1 expression; Functional mutation of Notch1 may trigger Notch1 overexpression in the rest cells of tumor by a till now unexplored mechanism, so that both functional mutation and overexpression of Notch1 may exist in the same tumors in different phases of tumor development.